200 BIOLOGICAL CHEMISTRY 



to be due to extracts from the foetus* or corpus luteum.f 



The reproductive organs furnish internal secretions which 

 regulate the development of the secondary sexual character- 

 istics, but the reader must be referred to other books for 

 further details. The interstitial cells of the testis correspond 

 in origin to the cells of the suprarenal cortex. 



From these observations we see that the chemical processes 

 in cells can be affected by chemical substances. When these 

 chemical substances are obtained from some source outside 

 the body they are called drugs, but substances formed inside 

 the body are known as internal secretions. The organs that 

 furnish internal secretions seem to be related to each other, 

 so that interference with one may upset the action of all. 



All cells add waste products to the circulating blood ; 

 some of these substances stimulate other cells to activity. 

 In the case of the ductless glands the production of substances 

 to stimulate other cells has become specialised, so that there 

 are aggregations of tissue with apparently no other function 

 than to produce hormones. Various intermediate stages such 

 as the pancreas, ovary and testis are known where the 

 function of producing an internal secretion is combined with 

 some other kind of activity. 



Chemical regulation is predominant where slow reactions 

 such as growth are concerned, whilst the 1 quicker reactions 

 are brought about by nervous influences. 



In plants chemical regulation must occur 'as is evidenced 

 by experiments on the dominance of the apical buds of 

 Picea excelsa. So long as these buds remain the geotropism 

 of other buds is inhibited, but after the apex is removed 

 another bud exhibits geotropism and inhibits the other ones.f 



The term hormone is used for the special substances that 

 affect activity without having any other obvious function, 

 but the substances which are excretory products and affect 

 activity as a subsidiary effect, such as urea and carbon dioxide, 

 are called parahormones. 



GENERAL REFERENCES 

 G. LUSK : Phlorizinglucosuria Ergebnisse der Physiologie, 1912, vol. 12, 



P- 315. 

 F. H. A. MARSHALL : The Physiology of Reproduction. Longmans, Green & 



Co., 1910. 



E. S. SCHAFER : The Endocrine Organs. Longmans, Green & Co., 1916. 

 S. VINCENT: Internal Secretions and the Ductless Glands. Arnold, 1912. 



* J. E. Lane-Claypon and E. H. Starling, Proc. Roy. Soc., 1906, 

 B. vol. 77, p. 505. 



f P. Ancel and P. Bouin, Soc. Biol., 1909, vol. 66, p. 605. 

 J L. Errera, Brit. Assn. Reports, 1904, p. 814. 



