Gustav Nylin’s Doctoral Thesis.

By Jørgen Malling Christensen.

Karl Gustav Vilhelm Nylin, 1892-1961, was a Swedish physician and cardiologist of international reputation. He published a large number of works in the field of cardiology and also about the physiology of school-age children and young people. Nylin was a great admirer of Malling-Hansen’s research into seasonal periodicity, and for his doctoral thesis he chose to replicate Malling-Hansen’s research. Between 1922 and 1930 Nylin served as a school physician in the Stockholm suburb of Spånga, and in this capacity he had an outstanding opportunity to use data from the pupils of 10 schools for his research. During the period 1926-29 he regularly weighed and measured the height of 2416 pupils, of which 1903 participated in the complete series of measurements and, thus, were included in his vast statistical material.

Nylin’s research consciously and consistently followed in Malling-Hansen’s footsteps, using similar techniques and methods (apart from the frequency of measurements). However, Nylin broadened the perspective by including also measurements of the standard metabolism and oxygen capacity of the blood of his research subjects. This was a logical and intelligent extension of the Malling-Hansen research agenda; and moreover: it served to make his research more congruent and relevant in relation to other contemporary international research in the period after Malling-Hansen’s death and the time of Nylin’s thesis. Nylin found that during the maximum periods of growth in height, the basal metabolism was also at a maximum level.

In addition, Nylin also added the aspect of light radiation, testing its use and effects on part of his research subjects.  In this, he may have been inspired or influenced by the example of Finsen, whose radiation institute in Copenhagen became world famous. Nylin found that the radiation had markedly strong stimulation effect on growth in terms of height, but that it decreased the growth in weight. Nylin points out that Finsen was the first researcher to show that hemoglobin levels (in adults) were also subject to seasonal variation. According to Nylin, in some of Finsen’s reports he discussed and made comparisons with those of Malling-Hansen.

Shortly after the successful defence of his thesis, Gustav Nylin visited the Royal Institute for the Deaf-Mute in October 1930 and gave a lecture entitled “The Present-day View of Malling-Hansen’s Research” (see “Lecture by Gustav Nylin in 1930”(in Swedish) on our website). In his lecture he praised Malling-Hansen for being  “...the first researcher to define and practise a precise, scientifically accurate research methodology”.

Moreover, he claimed that Malling-Hansen was:  “...the first to have analysed, with care and accuracy, the variations in height and length of school-age children, and to have found that their height decreases every day by 10 mm”.

He added that, apart from the French scientist Leclerc de Buffon (1707-1788) and Swedish physician Erik Vilhelm Wretlind (1838-1905), “...Malling-Hansen was the first to have found and documented a seasonal variation in terms of the growth of height and weight”.

These assessments come from a scientist of impeccable knowledge and reputation (Nylin); and what is remarkable is that Malling-Hansen was not even trained as a scientist, nor had he any medical or physiological training. In his ground-breaking research, Malling-Hansen was the first and the best of his period – and he was also a complete autodidact in this field!

Gustav Nylin has done us a great favour with his doctoral thesis: In his first chapter, “Historical Survey. Literature”, which follows this preface, he puts Malling-Hansen’s research into the perspective of similar and related research internationally back to the first contribution by Buffon in the mid 18th century and up to date (1929).

What emerges very clearly is that Malling-Hansen is part of a large array of researchers the vast majority of whom came after Malling-Hansen and to a large extent were inspired by him. His results were confirmed by Vahl, Camerer, Schmid-Monnard, Wiener, Carlier and Klaus Hansen in the 18th century, and by Porter, Schreiner, Schiøtz and Nylin during the period from 1900 until 1929.

According to chapter I of Nylin’s thesis, there were only three researchers before Malling-Hansen in this field: Buffon, Montbeillard and Andral, all of them French.

Contemporary with or following Malling-Hansen  Nylin mentions 60 other researchers/scientists who have done research similar to or closely aligned with that of Malling-Hansen.  These 60 scientists represent the following countries:Denmark: Vahl, Strandgaard, Lindhard, Johannsen, Finsen, Heerup

Norway: Hansen, Schiøtz, Schreiner (2 persons), Grundt, Kielland, Lunde, Bratt, Scheel, Føien

Sweden: Wretlind, Key, Sonden, Nylin

Finland: Rancken, Gripenberg, Grönberg, Tigerstedt, Olin

England: Kerr, Bleyer, Smith, Griffith

USA: Porter, Veeder, Rohlfing, Emerson, Burns, Benedict, Talbot, DuBois, McConnell, Fulton, Yagloglou, Kunde, Gustafsson

France: Carlier, Gavarett

Germany: von Krehl, Camerer, Monnard, Frank, Wimberger, Hartmann, Kestner, Peemöller, Gessler, Loewy, Jakowenko

Austria: Orel

Australia: Young.

Further details about the above scientists are in the footnotes added to Nylin’s text in his chapter I.

In summary: What we have in front of us is an entire new field of scientific research in physiology and metabolism, focused on periodicity. This research area started with Malling-Hansen and a few of his contemporaries. It has continued ever since, and Nylin has clarified the research field as it appears in the period from the 1880s until 1929. 

It is my belief that this field of research has been ongoing and expanded ever since then and is still very much alive today. It is up to us to follow the trail and identify the post-1929 researchers, their work and their results.

It is also conceivable that the periodicity found by Malling-Hansen and many others is a universal phenomenon which influences not only humans but animals, plants and other living organisms. Malling-Hansen famously included the trees in his own backyard as his investigation subjects!

When he died in 1890 he left behind a question which remains to be answered:What is factor X? Is the mysterious life-force linked to the sun, to the moon or to some other factor or set of factors in the universe? The search is bound to continue! Malling-Hansen was a pioneer, and he set the standards of research by means of his rigorous methods and procedures. His research remains ground-breaking and relevant.

A Swedish biography about Gustav Nylin can be read in Svensk biografisk lexikon.

            In a reformatory M. VAHL[4] of Denmark weighed 346 girls twice a year on 1st April and 1st October – he took no measurements of height.  From his investigations he concluded that increase in weight was greater during the summer than during the winter.  MALLING-HANSEN considers that this result, which seems to run counter to his own, is due to the fact that VAHL included in the summer period parts of the maximum period of weight-increase which he found himself.  Probably neither his own nor Vahl’s investigations will definitely prove whether or not the increase in July is as slight as MALLING-HANSEN  assumes, since neither of them carried out weighings during the summer holidays.  To VAHL’s investigations it may be objected that the girls were weighed in their clothes, but without hats or shoes. It is of course possible that their clothes were heavier in October than in April. It is noteworthy that MALLING-HANSEN found that  the children decreased in weight from March till June. The question may be raised whether this really is a physiological phenomenon.  As mentioned above, WRETLIND  had observed the same thing.

            MALLING-HANSEN considers that the periodic increase in weight corresponding to the different times of year are partly due to the changes in the water-content of the body. Naturally it is of particularly great interest to have this point settled. Much later, in 1919, RANCKEN[5] proposed the question whether the increase in weight observed in the sanatoria, which seem to be associated with certain seasons, are not dependent on the changes in the water-content of the body, which changes are in their turn affected by climatic factors.  RANCKEN quotes KREHL[6] and points out that our knowledge of water-metabolism is very obscure.  For a long time he carried out fairly close observations in himself as to variations in height, in connections with observations of the weather conditions.  He found that loss of weight from perspirations during the nights varied between 170 and 450 grams.  The loss of weight at the beginning of the holidays he considered to be due to the loss of moisture caused by increased physical movement.  He also showed that “critical loss of moisture” during term-time made its appearance in connection with changes in the weather. The weather and weight curves constructed by RANCKEN in 1919 show that the increase was smallest on those days when such invigorating climatic factors as sunshine, high barometric pressure, dry air and cold prevailed. Under depressing weather-conditions, such as darkness, damp, and heat, the increase in weight was greatest.

            MALLING-HANSEN has also touched upon the question of increase in weight in relation to diet.  He estimated the children’s appetites at various periods of the year by weighing the food they consumed.  Their appetites proved to be greatest in March, but then declined till June.  During periods of great increase in weight, as in the autumn, their appetites were not maximal.  He also observed that the boys ate more than the girls, but that their weight-increase was less.  The children were fed according to a pre-determined scheme.  Every week there were days when the children did not eat so much, as certain foods tempted them less.  Then MALLING-HANSEN eliminated this food and replaced it with milk and meat, which the children liked. Their weight then increased, but only for 21 days.  From this he drew the conclusion that more attractive food cannot affect the increase in weight of the children.  This conclusion would seem to be incorrect to some extent.  In such cases the result will probably be dependent on how well the children were nourished at the beginning of the experiment.  If the children were under-nourished, the weight-increase would probably be greater and very probably also cover a longer period.

            The French military doctor CARLIER[7] – who knew nothing of MALLING-HANSEN’s investigations – made the observation 1889-1893 that height and chest measurements increased more during the summer than during the winter half-year;  on the other hand weight-increase was greater during the latter period.

            In 1885 Professor AXEL KEY[8] published in Sweden his great work on the conditions of growth in the case of Swedish school-children.  This work greatly widened our knowledge and will probably be among the most remarkable which ever have appeared on this subject.  Of special importance are his conclusions as to the conditions of growth during the years of puberty. He shows that the period of puberty is characterised by increase in height for several years (pre-puberty) accompanied by slight increase in weight. Good increase in weight appears after the increase in height.  KEY considers that this relationship between the increases in height and weight is subject to certain laws (KEY’s law), and there is a striking agreement with the periods of growth during the different times of year found by MALLING-HANSEN.  KEY attaches exceedingly great importance to MALLING-HANSEN’s work.  In view of his own investigations, KEY propounds the question whether growth always takes place periodically, so that maximal and minimal periods in height-increase alternate inversely with periods in weight-increase.  As to the question of whether the periodicity discovered by MALLING-HANSEN is physiological or is due to changes in outward conditions, such as the school and diet of the children, etc., KEY is in doubt and “above all we must ascertain whether these same fluctuations similarly present themselves also in other places, and more specially under different climatic conditions and, the case of varying school organisations, with differently arranged holidays; or whether they are quite independent of the school &c.”

            These questions are still today only incompletely answered. In this connection KEY also considers that it would be of the greatest interest to elucidate the question whether the decrease in weight from March to June found by MALLING-HANSEN would actually be met with[9] if the holidays began earlier than the end of June.  KEY considers the periods of great height-increase, when the increase in weight is slight, to be critical periods in the development of children.  For he has found that the percentage of illness among the secondary-school children is greatest during pre-puberty, which period is characterised by great increase in height and slight increase in weight.

            W.CAMERER[10] (1893) and SCHMID-MONNARD[11] (1895) have made valuable contributions in support of MALLING-HANSEN’s observations.  In his work CAMERER publishes curves of the increase in height and weight of 8 children between the ages of 2 and 17. The investigations extended over several years, and measurements were taken on the following days: 1st January, 1st March, 1st May, 1st July, 1st September, 1st November, and again on 1st January.  His results show that the increase in height is minimal from September to November, increases in January, increases further till May, but then declines from May to July, and finally further declines somewhat during July to September.  On the whole, weight-increase was in the inverse order with a high maximum in September to November and a minimum in May to June.  CAMERER considers that on the whole his results agree with MALLING-HANSEN’s.  He calls the method of the latter the “generalising” in contradiction to his own, which he calls the “individualising”.  This designation is hardly justifiable, as instead MALLING-HANSEN’s method might be called both generalising and individualising – this so much more as the results have been arrived at by observing the same children. CAMERER does not accept MALLING-HANSEN’s hypothesis as to the influence of the warmth of the sun on growth.  He considers it improbable that the seasons could have any decided effect on growth, but rather that they, in his view, would make it more difficult for us to arrive at knowledge of the actual course of growth.  He shows that a marked alternation of large and small increases in height does exist and, in his summary, he also says that growth is periodic.

            SCHMID-MONNARD points out that WIENER, who only studied a single individual, could not show periodicity in height-increase. SCHMID-MONNARD himself took very careful observations of the increase in height in the case of 45 children under school age (2-7 years), 22 of whom were girls, and of schoolboys between the ages of 9 to 13 years.  The measurements were taken during the course of about a year, from June 1893 to August 1894, at intervals of from 3 to 6 weeks. A source of error in these investigations seems to be that these measurements were always taken between 4 and 6 p.m. – the operation thus extending over 2 hours. It does not appear from his description whether on each occasion the children were taken in the same order.

            SCHMID-MONNARD found that weight-increase was at its maximum during August to October. In February the children suddenly ceased to increase in weight, and during March they decreased.  Not until the end of June did they re-attain the weight that they had at the beginning of February.  During both August and September, when the children were going to school, their weight-increase was greatest; during July, when they had holidays, it was insignificant.  SCHMID-MONNARD considers that this goes to prove that school is not the cause of the slight increase in weight.  Moreover, the children who did not go to school showed the same results.  MALLING-HANSEN’s children had their holidays at about the same time as SCHMID-MONNARD’s. The increase in weight in the latter was better during June than during February to March, while MALLING-HANSEN, on the contrary, found the weight of his children decreased during the month of June. If this decrease is worked out for the period 20th May to 30th June, from the figures given in his tables, it proves to be 0.60 kg., which is a somewhat high figure.

            KLAUS HANSEN[12], Norway, 1895, gives a summary of 5 years’ weighings.  Weight-increase is calculated during the periods July to August, September to December, December to March, and April to June.  Like WRETLIND he found that during the school-months weight-increase was slight in comparison with that during the holidays.  SCHMID-MONNARD’s results, and more specifically the results of later investigators, show that this is hardly the case, and this disagreement will probably be due to the longer holidays and improved school-hygiene of more recent years.

            Among other things, SCHMID-MONNARD points out that the frequency of illness and death shows periodic variations, the former being greatest during the cold months and at the beginning of the year, and the latter from January to April. Autumn is said to be the “healthiest” season.  During the “unhealthy” months, e.g. January, occur the greatest daily variations from the mean value of the temperature of the months; during the “healthiest” month, September, temperature is most constant. He points out – as does MALLING-HANSEN – that even a slight drop in temperature causes a loss of weight on the following day.  SCHMID-MONNARD’s conclusion is that varying outward influences cause a periodicity “that the growth did not perhaps exhibit”.

            It was twenty years before anyone again began to make any detailed study of periodic growth.  However, in 1922 PORTER[13] published his work, in which he only dealt with fluctuations in weight.  For several years he weighed several thousand schoolchildren every month during term-time.  The children were weighed with their clothes on, but he considers that the weight of “indoor clothing” does not vary to any considerable extent at different periods of the year.  He then divided this material according to two principles.  He first grouped the children according to their ages in months, the average weight being calculated for each group and compared with the group nearest to it.  According to this method – the generalising method – weight was found to increase successively without any periodicity.  PORTER then divided the material into groups according to age and used the individualising method.  The increase in weight for each age-group separately was followed for several years.  Here he observed a marked periodicity. During the period June to December the increase in weight was considerably greater than during the period December to June, and this occurred regularly for many years.

            In 1922 SCHIÖTZ[14] published the results of an investigation on 70 boys between the ages of 12 and 16, and found that increase in height was greatest during January to May, and least during September to January.  During the last-mentioned period the increase in weight was greatest and, on the other hand, least during the period January to May.

            At the same time ALETTE and K.E. SCHREINER[15] published the results of measurements and weighings carried out on 223 boys and 139 girls between the ages of 12 and 18. The examinations were carried out on about the 25th January, 25th May, 1st October and again on 25th January and were continued every time for a week and were so arranged that the children were taken in the same order on every occasion.  The boys were examined in the morning and the girls in the afternoon.  The exact hour when the examinations took place is not given, as is the case with practically every similar examination in this field.  None but MALLING-HANSEN seems to have taken weights and measurements as far as possible at the same time on every occasion. SCHREINER’s investigations were particularly carefully worked up statistically.  The mean value of height and weight increases, and standard errors, standard deviations, and variation coefficients are calculated for each age-group.  It will probably be the first time that such statistics for similar examinations have been drawn up.  The children were divided into groups varying from 14 to 54 in each, so that each group was fairly small, and the standard error consequently fairly large. The results shown by the various groups are, however, in agreement.  They show that the increase in height is greatest during the spring term and least during the autumn term. SCHREINER also found that for girls from 16 to 18 years of age the increase in height during the autumn term was negative.  He is of the opinion that this is due to the fact that at the last examination the children did not draw themselves up sufficiently, but at the same time he says: “In many cases it was impossible to obtain the same height as on the previous occasion in October, although efforts were made to make them to stand erect.”  This might possibly be due to the fact that the last examination must have been at a considerably later hour than on the previous occasion. In all the groups he found that the increase in weight was greatest during the summer, less during the autumn term, and least during the spring term.  During the period last mentioned it was even negative for girls between the ages of 15 and 18.  SCHREINER also worked out height and weight relations according to ROHRER’s index[16] at the various periods and found the index lowest during the spring term, to increase later during the summer and autumn.

            In 1926 SCHIÖTZ published the results of another investigation into the growth of school children at different seasons. By means of measurements he followed the height and weight of 266 elementary schoolboys every month from and including 30th August 1922 up to and including 6th June 1923.  Further measurements were also taken on 20th June and 27th August, 1923.  The ages of the boys varied from 10 to 14 years, and the number of boys in each age-group varied from 36 to 63.  SCHIÖTZ found that the increase in weight rose during the period 27th September to 25th October and reached its maximum during the period 20th December to 17th January. The growth in height showed an increase during the period 25th October to 20th December and was at its maximum from 11th April to 9th May, which was maintained during the summer.  SCHIÖTZ made calculations according to ROHRER’s index at the different periods and found that the index rose somewhat from 30th August till 25th October and then declined till the 20th December, when it turned and rose gradually till the 14th March.  Subsequently it fell steadily to a minimum in June. SCHIÖTZ points out that from this the conclusion must not be immediately drawn that the Christmas and summer holidays are the cause of the rise in the index.  He emphasises the fact that the index value is high for a long time after the children have returned to school.  He will not call this “after-effects”, because, if such were the case, it would remain high for a longer time after the long summer holidays than after the short Christmas holidays – but here it is just the reverse.  In the same work SCHIÖTZ cites a similar examination of 31 boys in a boarding-school, “Toftes Gave”, where the results were the same, on the whole. There was, however, the difference that in the latter examination ROHRER’s index showed a maximum somewhat later in the autumn – in November – but the same maximum in March as was found in the case of the boys at Oslo.  SCHIÖTZ points out that autumn – the period during which the index rises and the increase in weight is more marked in relation to the increase in height – is a period of physical robustness.  School-teachers have also found that the autumn term is the best for teaching. On the other hand, spring, with its low ROHRER’s index, is a bad period.  In connection with his investigations SCHIÖTZ takes up the question whether it is possible to do anything to influence these low index periods.  Citing examples from the open-air schools, he considers that by means of hygienic measures, such as improved diet, change of surroundings, fixed bed-times, etc., it would be possible, even during the spring, to make the children put on weight considerably, i.e. to bring about a rising period in the index.

BENEDICT and TALBOT show that in the case of children of the same height and age, but of varying weights, the standard metabolism, calculated partly per unit of body surface and partly per unit of weight, is greater for the thinner than for the fatter children.  TALBOT considers fat to be a relatively inert substance, which plays no great rôle in the production of warmth in the body of a healthy organism at rest, for which reason he considers that an increase in the weight is followed by “a diluent of the calories”.  He is of the opinion that the amount of the protoplasmic[43] substance, presumably the albumen, determines the metabolism.

            The first considerable study carried out with a view to determine the metabolism during different periods of the year will probably be that of the English doctor, EDWARD SMITH[44] (1859). He states that the investigation was carried out during several successive days monthly, when the subject had an empty stomach. The CO2-production showed an increase during the spring from February to May-June, and then a decline during the summer and autumn.  With a rising temperature the CO2-production increased, while a rise in the barometric pressure caused a decline in the CO2-production.  SMITH states, however, that the correspondence was not striking, and it only occurred for short periods, but not when the average for longer periods was taken.  SMITH discusses the causes of the periodic variations in metabolism and, for the above-mentioned reasons, excludes temperature and atmospheric pressure, and assumes instead that sunlight may be the cause, since the metabolism demonstrably increased during the spring.

            In 1910 and 1912, LINDHARD[45] carried out comprehensive investigations as to respiration conditions during the different times of the year. Thus he made an expedition to Greenland from 1906-1908, during which he studied respiration during the different months of the year. The expedition was encamped on 76˚46’ N.L.  The climate is stated to have been typically arctic with a sharply marked period of darkness, during which the sun was not seen above the horizon.  Periodically during the year LINDHARD made daily observations on himself with respect to respiration frequency, alveolar carbonic acid tension, ventilation, and respiratory metabolism.  He found that the alveolar carbonic acid tension declined during the spring and summer, then rose successively to a maximum in January.  The same was the case with the respiration frequency, but the respiratory metabolism and ventilation, on the other hand, increased during the spring and summer. He did not, however, investigate the standard metabolism by determining the CO2-production. He remarks, however, that the CO2-figures ought to constitute a reliable measure of the metabolism, as his manner of living was subject to extremely slight changes.  His diet, for example, was the same all year round. From this he arrives at the conclusion that the respiration quotient was probably fairly constant. LINDHARD draws attention to the similarity between his results and the results arrived at by various investigators in “the high Alps”.  He says: “What is common to all these localities is the strong light, but not the rarification, nor the lack of oxygen, nor the amount of moisture, nor the temperature.”  Further he considers that: “Either substances are formed in the blood under the influence of the light, which reduce the threshold value of the carbonic acid tension, or the excitability of the centre is increased by reflex action.”

            Upon his return from Greenland, LINDHARD commenced a similar investigation in Copenhagen on six individuals, to discover whether the same periodicity was encountered also in a temperate climate.  The investigation was extended to the determination of the oxygen consumption. The respiration observations extended over 30 minutes. The persons experimented of, of whom only two were in a fasting condition, assumed a sitting posture with their arms resting on a table. LINDHARD found that the alveolar CO2-tension decreased during the spring and summer, but increased during the autumn and winter, as was the case in Greenland. In respect to the other functions of respiration, he found the same tendency as in Greenland. In the case of one of the persons experimented on (K.A.H.), the standard metabolism expressed in the oxygen consumed per kg. and hour proved to be fairly uniform during the year, while the other exhibited an appreciable seasonal variation, with successive increases of standard metabolism from January over the spring and into the summer, up to a maximum in August. Furthermore LINDHARD carried out an experimental study of the influence of light-baths on the respiration and found that the standard metabolism increased during the days immediately succeeding the light-bath.  LINDHARD concludes his consideration of his results thus: “The seasonal periodicity is due to the varying intensity of the sunlight.”

            In 1919 YOUNG[46], in Australia, investigated the standard metabolism of two persons during different periods of the year.  He found that their consumption of oxygen during the warm seasons of the year (November to April) was greater than during the cold season.  However, he does not return the standard metabolism in c.c. per kg. or per unit of body surface.  Besides YOUNG found that his own bodily temperature, measured in the rectum, was lower during the colder seasons of the year.  On particularly cold days, when the cold was unpleasant and produced shivering, the consumption of oxygen was increased.  In discussing his results, YOUNG assumes that the rise in standard metabolism during the summer may be partly explained by the increased oxygen consumption, in spite of the fact that the persons experimented on had rested for half an hour before the experiment. This result he considered to be due to the condition of the organism, not only in connection with the experiment but also in connection with conditions during the time immediately preceding it, so that, e.g. the amount of physical movement during the walk to the laboratory had a greater, so to say, after-effect during the warmer season of the year.  In 1924 McCONNEL, YAGLOGLOU and FULTON[47] found that in the case of a rise in the “effective temperature” the standard metabolism and the bodily temperature also rose.

            In 1923 KESTNER and HÄBERLIN[48] investigated the effect of the North Sea climate on a group of anaemic children who spent two months at the coast.  The standard metabolism was increased by the bathing, but they found that the mere visit to the coast had the same effect. The authors consider that the sun and wind had an irritating effect on the skin and thereby caused an increase in the standard metabolism.  In connection with these investigations, KESTNER and PEEMÖLLER[49] made the observation that irradiation with “Höhensonne” produces a brief increase in the standard metabolism.

            In 1925 GESSLER[50] published his interesting investigations on periodic changes in standard metabolism during the year.  Employing BENEDICT’s respiration apparatus, GESSLER carried out experiments on himself as regards oxygen consumption between 12 noon and 4 p.m. after fasting for 17 to 20 hours.  Before the experiment he had rested in a recumbent position for 30 to 60 minutes.  The experiments were repeated on several successive days during each month.  GESSLER calculated the mean values of the standard metabolism per kg. of weight and the mean value of the atmospheric pressure for each month, and he found a striking connection  between the two curves obtained, in that with a rising temperature during the summer a fall in the values for the standard metabolism presented itself, while during the winter, with a falling temperature, the standard metabolism increased.  In order to try to prove that the temperature really had such a marked effect on the standard metabolism, he also carried out some experiments on himself in respect of the changes in standard metabolism when the body was cooled owing to the experiments being conducted while his body was entirely naked.  These experiments showed that standard metabolism was increased as a result of the cooling of the body, and GESSLER formulates his conclusions thus: “When cooled the human being exhibits an increase of the O2-consumption (chemical regulation) which is not caused by muscular movement. In the case of similar external conditions this regulation is constant, but it changes with the change of the seasons of the year, in that it is higher in winter than in autumn and spring.” Thus GESSLER comes to the same conclusions as RUBNER[51] but is in conflict with LOEWY[52] and JOHANSSON[53], who, after particularly meticulous investigations, arrive at the conclusion that cooling of the body leads to a rise in the metabolism only when shivering takes place and, as a result, muscular movement presents itself.

            In 1928, during July and August, JAKOWENKO[54] carried out investigations in Eupatoria, on the shores of the Black Sea, as to the influence of climate, and he found that increase in wind and sunlight increased the standard metabolism. His results thus accorded with those of KESTNER cited above.

            In 1923 MARGARETE KUNDE[55] carried out standard metabolism experiments on herself daily during a period of one year. The experiments were carried out in a fasting condition after 30 minutes’ rest in a recumbent position with a constant room temperature during the whole year.  During the year she followed a varied diet. She calculated the mean value of the standard metabolism in total calories for each month.  There was an extremely slight variation of weight – 55 to 55.5 kg. – during the whole time, so that the reduction to calories  per kg. Of the weight was hardly necessary. From her investigation it appeared that the standard metabolism showed a minimum during the months of July and August.

            In 1923 COLLETT and LILJESTRAND found that a rise in standard metabolism presents itself during January-March, from which the authors assume that a seasonal variation in the standard metabolism does occur.

            FLORENCE GUSTAFSSON and BENEDICT[56] investigated the standard metabolism of 20 women between the ages of 18 and 20 at Wellesley College, Mass., during various periods of the year. The investigations were commenced in November 1926 and were concluded in January 1928.  The investigation was based on the determination of the consumption of oxygen of each woman once a month.  The objects of the experiment slept with their windows open the nights before the experiments, which were carried out the following morning before they had left their beds.  Proteid[57] food was avoided on the evenings before the experiments.  During the vacations – July, August, and September – no determinations were made.   Only 8 women continued the experiments during 13 months.  The mean value of the total oxygen consumption for these 8 women is calculated during the different months but is not given per kg. of weight, as the authors found that there was slight variation in weight from month to month.  From the table it appears that the standard metabolism rises during the spring and summer to a maximum in June. The low value during May is considered by the authors to be due to the fact that several of the women had their menstrual periods during that month, just at the time when the standard metabolism was investigated.  The authors point out that it would have been desirable for the investigation to be repeated on several successive days for each individual.  They consider that the causes of the variations in the standard metabolism were partly diet changes and partly violent physical movement (sport) and variations in sunlight.  They consider it to be doubtful whether temperature is the cause, as GESSLER points out, and recall LINDHARD’s opinion that sunlight exerts an influence at certain variations of the season.

            The latest work on the fluctuations in standard metabolism during different seasons of the year is one by GRIFFITH[58] and collaborators (1929).  During two years five individuals were kept under observation.  Their standard metabolism was determined repeatedly on successive days in each month for each individual.  The number of observations made on each individual during these two years was strikingly large and varied from 55 to 260.  The investigations were carried out when the objects of the experiments were in an entirely “postabsorptive” condition, when they had rested for 30 to 45 minutes in a recumbent position.  On the days before the determinations, violent physical exercise and albumen foods were avoided. The experiments were carried out every morning between 8 and 10. During the whole two years that the investigations were proceeding the room temperature was kept constant at about 25˚C.  The authors point out that the variability of the double determinations made on the  same day afford a measure of the error of the method, that the variability from day to day calculated per month is greater than the above-mentioned variability, and that the variability calculated per year is still greater.  This latter circumstance is considered to be evidence in support of a seasonal variation.  The total oxygen consumption and the calories per square meter, calculated by DU BOIS’ formula, showed a minimum in the summer for four of the individuals experimented on, and in the case of one of these four there was a fall in the standard metabolism during the spring.  The authors arrived at the conclusion that there was no certainty of the occurrence of a seasonal variation, but that there was presumptive evidence of one.  They point out that the causes of these variations need not necessarily be climatic conditions, but may be variations in food, physical exercise, or other unknown factors. This assumption they consider justified in view of the conflict between the results obtained at different times of the year by different authors, and particularly in view of the conflict between their own results and those of BENEDICT.  They point out that they found a minimum of pulse rate in the summer, in conflict with BENEDICT, who found the pulse rate at a minimum in the winter.

            NILS R. FINSEN[59] was probably the first to go thoroughly into the question of whether there is a seasonal hemoglobin variation in man.  In 1894 he published his periodical hemoglobin investigations for 20 men and 9 women.  The investigations were carried out with GOWER’s hemoglobin-meter.  FINSEN was fully alive to the sources of error connected with the determination of hemoglobin.  He indicates that short temporary hemoglobin changes present themselves as a result, inter alia, of the presence of large quantities of water, perspiration , and so on.  He examined the 9 women on two occasions, first at the end of the winter of 1893, and then during the following summer.  He found that the hemoglobin increased on an average 15% from the winter to the summer.  In the case of the men, who were for the most part medical students, he made monthly determinations.  The average number of blood determinations per individual was 7 to 8, and the maximum number per individual was 30.  FINSEN found that the hemoglobin increased month by month from December – January and attained a maximum in July-August-September.  He does not consider that the vacations had any influence on these results, as the maximum was already reached before the vacations began.  As causes of the variations he suggests, in the first place, a real increase in the amount of the hemoglobin of the blood, and in the second place, a periodic change in the concentration of the blood. He regards the first cause as the most likely.  He concludes his account with the following words: “The study of physiological periodicity is intimately connected with the study of the biological effects of the sun and the sun’s rays, as certainly as the sun gives rise to the change from day to night and summer to winter.”  This latter periodicity he considers directly or indirectly to condition the physiological one.

            But in 1928 H.J.HEERUP[60] carried out an investigation as to the influence of the light on 80 children and 20 training college students in the Färö Islands[61] in respect to the hemoglobin-content of the blood and the number of the red corpuscles.  The investigation was carried out on the same individuals at the end of February, when the darkest time was past, and at the end of September, when the effects of the light had ceased.  Contrary to expectation it proved that there was no provable difference between the results of the two determinations, although, as HEERUP points out, the children were paler in the winter.

Short summary of the literature.

            MALLING-HANSEN’s investigations, which were carried out over 40 years ago, will probably still today be the most comprehensive and thorough that have been undertaken into the growth of schoolchildren during the year; this chiefly because MALLING-HANSEN will be the only one to have observed meticulous measurement methods and to have taken records daily during several years.  The results show that the growth during the year is periodic.

            Subsequently less comprehensive investigations have been carried out on the periodic growth during the year, and on the whole they confirm MALLING-HANSEN’s results, especially the investigations of CAMERER, SCHMIDT-MONNARD, and SCHIÖTZ. 

            Like many other investigators, HAVEN EMERSON only made determinations of weight during different periods of the year. This last-mentioned author is the only one, as far as my knowledge goes, to deny any kind of periodicity.  That increase in weight is periodic during the year in the case of tuberculous individuals, children as well as adults, is shown by several investigations, of which STRANDGAARD’s will be the best.

            Several authors have demonstrated that standard metabolism is periodic during the year.  SMITH, LINDHARD and BENEDICT and GUSTAFSSON, have come to results that on the whole are in agreement, to the extent that standard metabolism shows a rise during the summer. The results of GRIFFITH and those of GESSLER are in conflict with the above-mentioned, as they find a decline in the standard metabolism in the summer as compared with the winter.

            BENEDICT and TALBOT’s and DU BOIS’ investigations as to standard metabolism and height-increase are the only ones that indicate that, during puberty, standard metabolism rises simultaneously with height-increase.  As far as I am aware there are no investigations where the same children have been kept under observation for a considerable time with frequent and simultaneous determinations of height, weight and standard metabolism.

            FINSEN’s investigation, which shows periodic changes in hemoglobin during the year in the case of adults, is probably the oldest and most important.  The results of HEERUP’s investigations are in conflict with FINSEN’s, but the latter were only carried out twice during the course of a year.