2o8 ELEMENTS OF BIOLOGY 



property in the preparation o£ hormones for use as treatment in 

 various human diseases. InsuHn may be obtained from islet tissue 

 in the fish and employed in the treatment of diabetes in Man; 

 adrenalin for human use is likewise prepared from the adrenal 

 glands of other animals. The most obvious explanation of this 

 interchangeability of hormones among vertebrates is that all have 

 been derived from a common ancestry. At least the evidence is 

 clear that all of the group are chemically related. 



Lastly, the effect of any hormone is the result of an interaction 

 between the hormone and certain cell protoplasms. For example, 

 the blood stream of a pregnant female mammal contains a hormone 

 from an ovarian structure that induces activity in the mammary 

 glands and the secretion of milk, but milk is secreted only by these 

 glands and not by other tissues. In other words, certain tissues may 

 be considered as attuned to these chemical influences and by their 

 response to the hormones act for the benefit of the animal as a 

 whole. Thus the hormones, transported by the blood, serve to unify 

 the organism, inducing such reactions in gland, brain, nerve, and 

 other tissues that serve the whole individual. 



The discovery of the existence of this intricate and sensitive sys- 

 tem of hormones in the human body has within recent years 

 brought a profound change in the concepts of human physiology. 

 As is so frequently the case with new discoveries, there has been a 

 tendency to overemphasize the endocrines and to ascribe to their 

 deficiency or overproduction all sorts of psychological and personal 

 traits. They have been called the glands of personality. While it is 

 undoubtedly true that abnormalities in the functioning of endocrine 

 glands have effects on these characteristics of the individual, it is 

 equally true that the abnormal functioning of other structures have 

 similar effects. Many diseases are characterized by rather definite 

 mental and psychological symptoms; cheerful optimism accom- 

 panies tuberculosis; on the other hand mental depression and irri- 

 tability are frequently associated with digestive disturbances. That 



