INTRODUCTION 7 



terest in the possibilities of endocrin biology. In 1912 Biedl, in the 

 second edition of his well-known monograph, "Die innere Sekretion," 

 published a systematic compilation of the literature. His bibliography 

 of some 212 pages included about seven thousand articles which dealt 

 directly with the endocrin glands. The rapid growth of the literature 

 at this time is evidenced by the fact that after the manuscript was sub- 

 mitted to the printer and before the book was through the press some 

 fifteen hundred new articles had appeared, necessitating the addition of 

 41 supplementary pages of bibliography. This brought the literature 

 up to 1913. There were then approximately 8500 titles in Biedl's list. 

 There is no available record of the number of papers appearing during 

 the period from 1913 to 1916, but, judging by the number of articles 

 preceding and following this period, four thousand might be regarded as 

 a safe estimate. During the period of the war the output in this field 

 was of course restricted, but even during this time several hundred 

 articles appeared each year. Since the war the output has again in- 

 creased. At the present time the journal Endocrinology, which attempts 

 to list all original articles in the field, is publishing about fifteen hundred 

 titles a year. 



Nature of the Internal Secretions 



As an example of a typical hormone "secretin" may serve. This is 

 a substance formed in the mucous wall of the duodenum by the action 

 of the chyme on an antecedent "prosecretin." The secretin is absorbed 

 into the blood and carried to the cells of the pancreas and perhaps the 

 liver, and these organs aTe thereby excited to secretory activity. Pos- 

 sibly a more striking example was afforded a few years since by the 

 so-called "Bohemian twins," the Blazek sisters of Continental museum 

 fame, whose case was reported by Trunecek (1910). The bodies of these 

 women were united along one side, i.e., they constituted a living pygop- 

 agus monster, so that while they were otherwise independent organ- 

 isms, the blood stream was in a measure common to both. When one of 

 the twins became pregnant the mammary glands of each hypertrophied, 

 and after the infant was born each was able to nourish it. The most 

 plausible explanation for the phenomenon is that during the development 

 of the fetus something was contributed to the common blood stream which 

 stimulated the mammary tissues of both woinen. 



Such examples of bodily reactions to circulating chemical substances 

 are by no means unique, nor are the endocrin glands the only source of 

 such active materials. One of the most important regulatory substances 

 of this kind is carbon dioxid. This gas is formed as an end product of 

 oxidation in all the cells of the body, but particularly in the muscles. 

 Whenever the muscular activity is increased the carbon dioxid concen- 



