life: its nature^ origin, and maintenance SCHAFER. 521 



comes iuio contact with these cells it converts their })rosecretin into 

 ''secretin." This is a liormonc which is passed into the blood and 

 circulates with that fluid. It has a speciflc efteet on the externally 

 secreting cells of the pancreas and causes the rapid outpouring of 

 pancreatic juice into the intestine. This effect is similar to that of the 

 hormones of the pituitary body upon the cells of tlic kidney and mam- 

 mary gland. It was discovered by Bayliss and Starling. 



INTERNAL SECRETIONS OF REPRODUCTIVE ORGANS. 



The reproductive glands furnish in many respects the most interest- 

 ing example of organs which — besides their ordinary products, the 

 germ and sperm cells (ova and spermatozoa) — form hormones which 

 cii'culate in the blood and effect changes in cells of distant parts of the 

 body. It is through these hormones that the secondary sexual char- 

 acters, such as the comb and tail of the cock, the mane of the lion, the 

 horns of the stag, the beard and enlarged larynx of a man, are pro- 

 duced as well as the many differences in form and structure of the body 

 which are characteristic of the sexes. The dependence of these 

 so-called secondary sexual characters upon the state of develop- 

 ment of the reproductive organs has been recognized from time im- 

 memorial, but has usually been ascribed to influences produced 

 through the nervous system, and it is only in recent years that the 

 changes have been shown to be brought about by the agency of in- 

 ternal secretions and hormones, passed from the reproductive glands 

 into the circulating blood.' 



CHEMJCAL NATURE OF HORMONES. 



It has been possible in only one or two instances to prepare and 

 isolate the hormones of the internal secretions in a sufficient condition 

 of purity to subject them to analysis, but enough is known about 

 them to indicate that they are organic bodies of a not very complex 

 nature, far simpler than proteins and even than enzymes. Those 

 which have been studied are all dialysable, are readily soluble in 

 water, but insoluble in alcohol, and are not destroyed by boiling. One 

 at least — that of the medulla of the suprarenal capsule — has been 

 prepared synthetically, and when their exact chemical nature has 

 been somewhat better elucidated it will probably not be difficult to 

 obtain others in the same way. 



From the above it is clear that not only is a coordination through 

 the nervous system necessary in order that life shall be maintained 

 in a normal condition, but a chemical coordination i.s no less essential. 

 These may be independent of one another; but on the other hand 

 they may react upon one another. For it can be shown that the 

 production of some at least of the hormones is under the influence of 



' The evidence is to be found I'n F. H. A. irarshall, Tlie I'iiysiology of Keproductiou, 1911. 



