Malling-Hansen’s Research into Seasonal Variations in the Growth of Children - an Overview and an Update, April 2017.

Research and comments by Jørgen Malling Christensen.

Illustrations by Sverre Avnskog.

 

Research for a good purpose.

 

When Rasmus Malling-Hansen initiated his weighings and measurements of a small group of pupils – only 23 - in 1877, his motivation was shaped by practical purposes and by his strong sense of care for the children of the institute: His aim was to find the best possible diet in terms of ensuring their good health. This was in tandem with other, similar, changes he had instituted since he was appointed principal in 1865; for example he increased the time available for outdoor play; made sure that all pupils would work in the orchard of the institute, helping to grow their own vegetables, herbs and fruit, in the process getting fresh air, exercise and sunshine; and he improved the indoor climate also, by means of better ventilation.

 

Nutrients and metabolism were not yet well understood

 

Malling-Hansen’s pioneering research should be understood against the background of the very limited understanding of nutrition and nutrient elements in the world in 1877: We must keep in mind that science was only on the verge of discovering and understanding nutrients such as vitamins[1], proteins and minerals. The understanding of fats, carbohydrates and other macro and micro nutrients was non-existent among the population at large and very limited even among the most advanced scientists.

 

Hence, Malling-Hansen could not find guidelines or answers in the scientific literature, nor could he obtain any authoritative or well-grounded information in the circles of scientific experts of the time. On the question of the best possible diet, he did receive advice from Professor Peter Panum[2], and it appears to have been Panum who initially suggested Malling-Hansen to conduct his own studies. But it was also in Malling-Hansen’s nature to be inquisitive and thorough, and he had a strong self-confidence. So, undaunted by the immensity of the task, he set out to experiment with various combinations of what he called the “regimen” (the institutional diet).

 

Unexpected results

 

His expectation was that the experiments conducted 1877-78 would show what kind of food combination would lead to steady, uninterrupted and healthy weight gain (growth) in the children and to a general improvement of their health. He did not expect that which he found: that irrespective of their food supply and their degree of physical activities, the growth of the children was not regular or linear over time, rather it was startlingly seasonal and jumpy! The belief and the assumption at the time – shared by common people as well as by scientists – was that children and young people (under normal conditions of good health and good food) would grow at a regular pace, evenly maintained throughout the year, and Malling-Hansen was the first to find a seasonal pattern.

 

Malling-Hansen mentions in Fragment I (1883) that he originally planned to conduct his experiments for only one year. However, the unexpected results of his weighings and measurements, using rigorous scientific methods and analyses, were so surprising that they spurred him on. We know from the surviving notebooks, recording the data of the measurements and weighings, that he continued this line of research on and off up until his premature death in September 1890. It is very likely that he planned to publish a “Fragment 4”, but he died before he could accomplish this task.

 

Reasons for the continuation of the research

 

The reasons for continuing the experiment after the initial findings in 1877-78, increasing the scale to eventually include most of the 130 pupils of the institute, were probably a combination of the following factors:

 

1) He became frustrated and intrigued by the initial findings that there seemed to be no clear causality between the quality and quantity of the diet on the one hand[3] and the weight gain/bodily growth on the other hand. Rather, weight gain and growth was seasonal and occurred in jumps – in periods he found it to be negative or at a complete stand-still – and he could not fathom the reasons why.

 

2) Malling-Hansen’s scientific curiosity was aroused; what started as an experiment with a decidedly practical purpose gradually developed into something else. The practical purpose – to find the best diet – was never abandoned, but to this was added his search for “Factor X” – the elusive cause behind the seasonal pattern of growth. Alas, he died before he found Factor X. As we shall see later on, scientists all over the world have, since then, continued the search for the Factor X!

 

Four important factors helped him along

 

Malling-Hansen’s research project was greatly supported by at least four circumstances:

a) He enjoyed the trust of his immediate superior in the Ministry of Education, Director J.P. Trap[4], who interfered very little in the daily affairs of the institute and delegated most of the responsibility and decisions to his trusted principal. When Wolfhagen[5] took over the directorship in late 1884, Malling-Hansen’s position and possibilities deteriorated. If Wolfhagen had been his superior officer in the 1870s and first half of the 1880s, I assume that he would not have permitted Malling-Hansen to use that much time and resources to the research activities; however, Wolfhagen probably felt (in 1884 and following years) that he could not forbid Malling-Hansen to continue his research, since he had obtained public financial support on several occasions, and since Malling-Hansen had successfully presented his findings at the International Medical Congress in Copenhagen in 1884.

b) Malling-Hansen was privileged in the sense that he received funding from the Carlsberg Foundation and from the Danish government for his scientific research. Thus in 1882 he received 4000 kroner and in 1885 another portion of 4000 kroner from the Carlsberg Foundation. In his November 1885 application for funding he mentioned that he had received 6000 kroner from the Danish government. This funding enabled him to acquire the proper equipment, have urine samples from the pupils regularly analysed and to publish his results – Fragment I in 1883, Fragment II in 1884 and Fragment III a and b in 1886.

 

c) Malling-Hansen was fortunate that the International Medical Congress was held in Copenhagen and at a point in time (August 1884) when he had had time to gather sufficient evidence to be able to be allowed to present his findings to this audience and to the world. He made very good use of this excellent opportunity, and his presentation was received with much attention and respect by the international medical elite. This was followed up and further stimulated by numerous articles in foreign newspapers and journals (see the articles published on our site).

 

d) As the principal of a boarding institution with around 130 pupils, Malling-Hansen was in the rather special (and privileged) situation of being able to weigh and measure all pupils daily over a long period of time. In order to replicate his study – or to disprove his results – other scientists would have had to find similar stable research objects, which could be followed and monitored daily in one single institution and over a long period of time. Rather few scientists would have that favourable situation.

 

School hygiene

 

During this period - the 1870s and 1880s  - there was a worldwide general and strong interest in the issue of what was called “school hygiene” – a broad concept used by medical science, by educationalists and by politicians of that period to cover everything connected with the health and welfare of school children. Hence, Malling-Hansen was by no means alone in this point of focus, and this general interest in “school hygiene” and in Public Health issues certainly stimulated the interest in Malling-Hansen’s research.

 

There were also a small number of other scientists and heads of schools and institutions who carried out similar studies – in Denmark. Malling-Hansen mentions (in Fragment I) two such studies in Denmark:

 

1) Over a period of 9 years, the principal of a foundation for girls and young women (Jægerspris), Dr Martin Wahl (1827-1887)weighed all boarders individually twice per year;

 

2)Otto Nicolai Jensen (1840-1915), principal of a similar institution for boys (“Det Kongelige Opfostringshus”) weighed all boys once a month over a period of 18 months.

 

The uniqueness of Malling-Hansen’s research

 

However, compared to these two cases, Malling-Hansen’s method was much more detailed, thorough and rigorous, as from 1882 weighing all 130 pupils daily and measuring their height over a period stretching until the beginning of 1886.  

 

The other important difference is that Malling-Hansen also measured biological growth – the seasonal growth of trees – in an attempt to find natural laws for all biological growth. It is clear from his Carlsberg Foundation funding application of January 4, 1883, that he was trying to find out whether the moon or the other planets of our solar system could have something to do with the unknown Factor X.

 

What also makes Malling-Hansen’s approach unique is that he made use of international meteorological data from stations all over the world. He was trying to ascertain if there was, indeed, a global phenomenon that determined the rate of growth of the human body (and ultimately of all biological growth[6]).

 

While Malling-Hansen started his physiological research as a local, institution-based project, over time he expanded it to have a global scope! He probably reasoned that if there was a universal growth factor X, the effects of which he had found and proven on his own pupils, then this universal factor – emanating from celestial bodies and unknown forces – would obviously also have similar effects on all other children on earth and on all living species.

 

The idea was exceedingly bold, but it was not crazy! After all, the natural phenomena and laws which science has discovered in the course of the last three centuries have an impact on all life on earth. And obviously some of these natural phenomena have their origin and causes in universal forces in the immediate surroundings of planet Earth. Obvious examples are: Gravity; effects from the moon on ebb and tide; solar heat, flares and storms; effects from other planets in our solar system; forces connected with our place in the Milky Way and forces from the galaxy (some of which may not yet be known).

 

Malling-Hansen’s ideas were not farfetched! And their foundation consisted of his rigorous research producing reliable data and using strictly empirical, objective methods. Though he had never had any scientific training, Malling-Hansen learned by doing and by using his own intellect and power of reasoning[7]. He probably also received good advice about research methods from Peter Panum and from the giant of Danish science at the time, Japetus Steenstrup[8]. Malling-Hansen had personal contacts with Steenstrup, who was an uncle of Malling-Hansen’s second wife, Anna Steenstrup.

 

Malling-Hansen’s Research Project Stopped with his Demise

 

After the publication of “Fragment III a and b” in 1886, Malling-Hansen continued his weighings and measurements, albeit at a smaller scale, filling out countless notebooks with the results and proceeding to analyse the results. His main aim was, of course, to identify the elusive Factor X, which he believed was behind the mysterious seasonal pattern of bodily weight gain and growth of children (and of all living things).

 

However, the last four-five years of his life were dogged by ill health and by his many stressful official duties and problems. Malling-Hansen suffered from a heart condition which eventually caused his stroke in September 1890. The progress of his scientific work was also hampered by his many duties, not only as a very busy principal but also as secretary of the ministerial commission that planned for the future organisation of education for the deaf-mute, the blind and the mentally handicapped[9]. He also had a key role in the planning of the new institute for the deaf-mute at Nyborg, inaugurated in 1891, after his death.

 

Much time and energy was also taken up by his conflict in 1884 and 1885 with his superior, Friedrich Hermann Wolfhagen, who had assumed office in the autumn of 1884. Likewise, he suffered a disappointing setback when much of his planning for extending and improving his institute was brutally and in humiliating manner axed by the royal building inspector, the influential architect Ferdinand Meldahl[10] in September 1883.

 

Since Malling-Hansen was – even in his last five years – a brilliant writer as well as public speaker, he was constantly sought after for giving speeches and formulating reports and plans. His oratory talents made him speaker of the freemason lodge during his last two years, and surely this responsibility – however important and dear it was to him – also taxed his energy and health.

 

The period from approximately 1887 to 1890 was also the period when Malling-Hansen dedicated time and energy to learning the new artificial language Volapük and to help developing its use in Denmark. He learned it well enough to be able to translate from Danish into Volapük and vice versa; he started Volapük clubs and he gave lectures about the benefits of this international language[11].

 

As mentioned above Malling-Hansen continued, also after the publication of “Fragment III a and b” in 1886, to collect and analyse data about the seasonality of weight and height development of children. However, his short remaining lifespan and his frail health did not allow him to publish any follow-up work, and we have, as of now, no indication that he got any further in his search for Faxtor X than what has been documented in Fragment III a and b.

 

However, as we shall see in the following, other scientists have since his time continued his line of research. This line of research remains active to this day.

 

Strandgaard[12]: Seasonal Pattern of Weight Fluctuations in Tuberculosis[13] Patients.

 

Niels Julius Strandgaard was a Danish physician who dedicated his life to the treatment and research on tuberculosis. He published an article in the Danish Journal “Hospitalstidende” on April 1, 1914. We have not yet found the original article, however it was important enough to be mentioned and quoted in the medical journal “The Lancet” of June 13, 1914, and the Lancet article is on our website.

 

For our present purposes, the interesting aspect is that Strandgaard investigated weight gain (and loss) of his TB patients and found a marked seasonal pattern of weight gain. He surmised that the weight gain was correlated to the relative humidity of the atmosphere and to the air temperature. He reported that his results of 10 years of research were strikingly similar to the seasonal pattern obtained by Rasmus Malling-Hansen. The Lancet article also mentions other contemporary physicians and researchers obtaining similar results, namely H. Adsersen[14]; and Bondeson and Jörgenson. To these scientists working in the tradition of Malling-Hansen around the turn of the century should be added Dr Hans Jakob Hansen, 1865-1930 (see footnote below).

 

Gustav Nylin and his doctoral thesis

 

Karl Gustav Vilhelm Nylin, 1892-1961, was a Swedish physician and cardiologist of international recognition. He was a great admirer of Malling-Hansen’s research, and as a young school physician in a Stockholm suburb he replicated Malling-Hansen’s research in 10 schools under his responsibility. From 1926 until 1929 he regularly weighed and measured 2416 pupils, of which 1903 were included in the complete series of measurements. Hence, Dr Nylin obtained a vast statistical material and this became his doctoral thesis: “Periodical Variations in Growth, Standard Metabolism and Oxygen Capacity of the Blood of Children”, successfully defended in January 1930 at the Karolinska Institute, Stockholm.

 

Dr. Nylin used the same techniques and methods as Malling-Hansen, and, in addition, he broadened the perspective by including measurements of the standard metabolism and oxygen capacity of the pupils. This was a logical and clearly relevant extension of the Malling-Hansen research agenda.

 

Dr. Nylin found the very same seasonal pattern as that of Malling-Hansen in terms of weight and height. Moreover, he also found that during the maximum periods of growth in height, the basic metabolism was also at a maximum level.

 

Dr. Nylin also added the aspect of light radiation and its effects; he found a correlation between the amount of light and growth in terms of height.

 

The latter aspect leads us to another important scientist, namely the Danish-Faroese physician and physiologist Niels Ryberg Finsen (1860-1904), the first Dane to win a Nobel Prize (1903). In his doctoral thesis, Nylin points out that Finsen was inspired by Malling-Hansen and that he referred to RMH’s research in some of his reports. Finsen was primarily interested in the biological effects of light and experimented with phototherapy (light radiation) as a cure for various cutaneous conditions, primarily lupus vulgaris. Finsen is regarded as one of the founders of radiotherapy, also known as radiation therapy or RT/RTx/XRT (other founders being Marie Sklodowska Curie,1867-1934, and Wilhelm Röntgen, 1845-1923).

 

In his research Finsen demonstrated the seasonal variations of haemoglobin in human blood. He found that haemoglobin[15] levels increase, on average, by 15% in summertime, compared to winter period levels. Finsen concluded his investigation with these words[16]:

“The study of physiological periodicity is closely connected with the study of the Sun and with the biological effects of sunlight, as surely as the Sun causes the fluctuations of day and night, summer and winter.”

 

In 1930 Gustav Nylin visited Copenhagen and gave a lecture about Malling-Hansen’s and his own research (see on our website: “Lecture by Gustav Nylin in 1930”). In his lecture, Nylin praised Malling-Hansen for being “...the first researcher to define and practise a precise, scientifically accurate research methodology”. Moreover, he stated that Malling-Hansen was: “...the first to have analyses, with care and accuracy, the variations in height and length of school-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 the 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”.

 

The first chapter of Nylin’s thesis is on our website (“A Swedish Scientist in Malling-Hansen’s Footsteps”). This chapter is a marvellous source of information, because here Nylin records the names of other important scientists who followed in Malling-Hansen’s footsteps, continuing this particular field of research. He lists the names and nationalities of 56 scientists:

 

Denmark: Martin Vahl, Niels Julius Strandgaard, Jens Peter Johannes Lindhard, Wilhelm Ludvig Johannsen, Niels Ryberg Finsen, Hjalmar Heerup.

 

Norway: Klaus Hansen, Carl Schiøtz, Alette Schreiner, E. Grundt, Hjalmar Høegh Kielland, N. Lunde, J.F. Bratt, O. Scheel, Thomas Føien.

 

Sweden: Erik Vilhelm Wretlind, Axel Key, Klas Gustaf Anders Sonden, Karl Gustav Vilhelm Nylin.

 

Finland: Rancken, Rita Gripenberg, J. Grönberg, Robert Adolph Armand Tigerstedt, Hanna Olin.

 

England: James Kerr, A. Bleyer, Edward Smith, Frederick Griffith.

 

USA: W. T. Porter, Borden S. Veeder, E. H. Rohlfing, Haven Emerson, N. B. Burns, Francis Gano Benedict, Fritz B. Talbot, Eugene Floyd Du Bois, William John McConnell, Fulton, Yagloglou, Margarete Kunde, Florence L. Gustafsson.

 

France: Carlier, Louis Denis Jules Gavarrett.

 

Germany: Ludolf von Krehl, Johann Friedrich Wilhelm Camerer, Karl Schmid-Monnard, Hildegard Frank, Wimberger,A. Hartmann, Otto Kestner, Friedrich Peemöller, H. Gessler, Adolg Loewy, W. A. Jakowenko.

 

Austria: Herbert Orel.

 

Australia: Young.

 

Everett L. Marshalls[17] updated List of Researchers

 

In the June 1937 issue of “The Journal of Pediatrics” the American psychologist Everett L. Marshall published an article, in which he reviewed and summarised 23 studies by American scientists, all of them replicating Rasmus Malling-Hansen’s pioneering research – or, at least, carrying out research along the same line, seeking to verify or not verify a seasonal pattern of growth. For details, we refer to the article which is on our website.

 

Some of these researchers found a seasonal pattern akin to that found by Malling-Hansen, others did not; however, the point to underline here is that Dr. Marshall has done us a great favour by reviewing and summarising the research in this field, because his article provides us with names, titles and the year of publication of those who followed in Malling-Hansen’s footsteps and, hence, is a valuable addition to the list of researchers provided by Dr. Nylin in his 1929 thesis.

 

The researchers listed (and not previously mentioned by Dr Nylin) are:

 

Richard E. Scammon, 1927

 

Barker Sanders, 1934

 

F. W. Hitchings and G. W. Fitz, 1901

 

Harold K. Faber, 1920

 

Joseph Berkson, 1930

 

Ruth Sawtell Wallis, 1931

 

Hughine McKay and Mary Ann Brown

 

L. E. Holt, 1918

 

Emmet Holt and Helen L. Fales, 1923

 

John C. Gebhardt, 1924

 

W. T. Porter and P. C. Baird, 1927

 

Harry N. Gould 1930

 

Margaret Chaney and Margaret Justin, 1928-30

 

Carrol E. Palmer, 1933

 

C. B. Davenport, M. Steggarda and W. Drager, 1934

 

Jessie Whitacre, 1935.

 

Further details, such as titles of their research reports, are found in the Marshall article.

 

Carroll Edwards Palmer Replicating Malling-Hansen’s Research in 1933

 

C. E. Palmer[18], 1903-1972, was a towering figure in public health, particularly in regard to research on the diagnosis, treatment and prevention of tuberculosis. He initially served as a consultant at the US Public Health Service and as from 1942 as the director of the Tuberculosis Research Program. In 1949 Palmer was appointed director of the World Health Organisation Tuberculosis Research Office of the United Nations.

 

Between 1923 and 1928 Palmer carried out monthly weighings of 2,500 schoolchildren of the ages 6 to 16. His aim was to investigate whether there was a seasonal pattern of growth. Palmer did indeed find a seasonal pattern similar to the one found and documented by Malling-Hansen[19].

 

However, our purpose in the context of this article is not to go into details about Dr Palmer’s results. Our interest lies in the fact that he did, in fact, continue Malling-Hansen’s line of research; and our second focus is on Palmer’s references at the end of his article, because they add to our list of scientists who have followed in Malling-Hansen’s footsteps, continuing this particular line of research.

 

Palmer’s references are:

 

R. Martin, 1924 (Germany)

 

A. A. Mumford, 1912-14 (UK)

 

Ada G. Paterson and E. Marshall, 1927 (New Zealand)

 

C. M. Jackson, 1931 (USA)

 

G. Wolff, 1932 (Germany)

 

F. Boas, 1898 (Canada)

 

S. Schiøtz, 1923 (Norway)

 

F. Gray, 1910 (USA)

 

Louis Schwartz, R. H. Britten and L. R. Thompson, 1928 (USA)

 

C. B. Davenport and Blanche M. Minogue, 1930 (USA)

 

T. W. Todd, 1930 (USA)

 

C. B. Davenport, 1926 (USA)

 

L. K. Frankel and L. L. Dublin, 1916 (USA)

 

W. T. Porter, 1893 (USA)

 

F. Boas and C. Wissler, 1906 (USA)

 

H. G. Richey, 1931 (USA)

 

F. Boas, 1932 (USA)

 

S. D. Collins, 1931 (USA).

 

The titles of the above research reports are found in our article about Dr Palmer’s research results.

 

A Contemporary Danish Study of Seasonal Variations in Growth and Body Composition

 

“Pediatric Research”, volume 79, no. 2, issue of February 2016 has a very important and interesting article: “Seasonal variations in growth and body composition of 8-11-y-old Danish children”. The article presents a succinct summary of a fascinating piece of research, continuing and developing the line of research initiated by Rasmus Malling-Hansen in the 1870s and 1880s!

 

The full text of the abstract is now free to use! It can be found on www.nature.com/pr/journal/v79/n2/index.html It is rather technical, but I recommend it highly for its clarity, brevity and relevance in relation to the RMH research. It is clearly a landmark!

 

The research team[20] behind the study is from the Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen.

 

Some 140 years ago, when Rasmus Malling-Hansen initiated his research into children’s gains in height and weight, he did so – as pointed out in the opening parts of this article – with the aim of finding the best possible nutrition for the school-children under his care. There is an interesting parallel here, when comparing with the objectives and the contextual conditions of the Danish research team; because their particular piece of research – “The OPUS School Meal Study” – is an important element in the overall context of the “New Nordic Diet” and the OPUS project.

 

The purpose of the OPUS school meal intervention is to investigate the effect of the “New Nordic Diet”[21] on the well-being, development and state of health of schoolchildren. More details are found on www.foodoflife.ku.dk/opus Under OPUS, 300 healthy recipes have been developed, and the meals are tailored to the food patterns of children aged 8 to 10.

 

The article in “Pediatric Research” is a very short summary of the results of the research carried out between August 2011 and June 2012. 760 children from nine schools between the ages of 8 and 11 were included. Measurements were taken every three months of weight, height, body mass index (BMI),fat mass index (FMI) and fat-free mass index (FFMI)and the team searched for possible seasonality.

 

The findings suggested (but did not prove indisputably) seasonality in growth and body composition.  However, the findings for height were in agreement with results from previous studies – among them Rasmus Malling-Hansen’s study published in 1886 and which is mentioned as the first of the scientific references!

 

From the point of view of the International Rasmus Malling-Hansen Society, of primary interest in this context are these three aspects:

 

1) Rasmus Malling-Hansen’s groundbreaking research, undertaken from 1877 and well into the 1880s, continues to be relevant and remains a scientifically recognised point of departure even for contemporary research in this area;

 

2) This particular line of research – seasonality of growth of the human body - has been ongoing ever since Malling-Hansen’s time and is still ongoing! It has been and is undertaken in several parts of the world; this field of research is alive! And the reasons behind seasonality have not yet been found!
Malling-Hansen was searching for what he called “Factor X”. Factor X has still not been found, but its effects continue to show up!

 

3) The OPUS research team has done us the great service of providing a summary of previous research on the first page of their article; furthermore, their list of references provides  further clues and is very helpful in terms of identifying relevant scientists and their research papers. For full details we refer to the last page of the article. However, it is meaningful here to list the most relevant of these names, together with their year of publication, since this list is a natural update to the previous lists of researchers, mentioned above.

 

Their references are:

 

1. R. Malling-Hansen, 1886

 

2. E. R. Bransby, 1945

 

3. W. A. Marshall, 1971

 

4. J. B. Orr and M. L. Clark, 1930

 

5. E. L. Reynolds and L. W. Sontag, 1944

 

6. E. Takahashi, 1966

 

7. H. Emerson, 1927

 

8. T. W. Porter, 1920

 

9. S. Kondo, E. Takahashi, K. Kato, S. Takahashi, M. Ikeda, 1978

 

10. M. Ikeda and T. Watanabe, 1985

 

11. L. Gelander, J. Karlberg, K. Albertsson-Wikland, 1994

 

12. V. Tillmann, N. K. Thalange, P. J. Foster, M. S. Gill, D. A. Price, P. E. Clayton, 1998

 

13. L. Gelander, W. F. Blum, L. Larsson,  S.Rosberg, K. Albertsson-Wikland, 1999

 

14. C. Land, W. F. Blum, A. Stabrey, E. Schoenau, 2005

 

15. D. I. Shulman, J. Frane, B. Lippe, 2013

 

16. T. Baranowski, T. O’Connor, C. Johnston, et al, 2014

 

17. A. X. Rodriguez, N. Olvera, P. Leung, D. P. O’Connor, D. W. Smith, 2014

 

18. R. Luboshitzky, D. Yanai, Z. Shen-Orr, E. Israeli, P. Herer, P .Lavie, 1998

 

19. R. Valcavi, M. Zini, G. J. Maestroni, A. Conti, L. Portioli, 1993

 

20. S. Cahill, E. Tuplin, M. R. Holahan, 2013

 

21. L. Marco-Gracia, F. B. Ortega, J. R. Ruiz, et al, 2013

 

22. M. F. Hjort, J. P. Chaput, K. Michaelsen, A. Astrup, I. Tetens, A. Sjödin, 2013

 

23. C. T. Damsgaard, S. M. Dalskov, R. A.Petersen, et al, 2012

 

24. C. T. Damsgaard, S. M. Dalskov, R. P. Laursen, et al, 2014.

 

From the point of view of the International Rasmus Malling-Hansen Society our task is to continue to keep abreast of contemporary research in this field, as well as to document previous relevant research projects in so far as they are relevant to Malling-Hansen and his research contributions.

 

---