THE ADRENAL GLAND 269 



The physiological processes by which any significant change in the 

 composition of the body fluids is resisted or adjusted to the needs of 

 the moment are often termed compensatory mechanisms. These physio- 

 logical mechanisms are of many kinds : heat regulation by the skin and 

 lungs, the regulation of water, hydrogen ion and electrolyte concentra- 

 tions by the kidneys and lungs, and one which is the subject of the 

 present discussion. This is the activity of the endocrine glands which 

 regulate the composition of the fluid environment not only by the action 

 of their products on the excretory organs but also by the effect of these 

 secretions on the chemical processes within the cells themselves. 



The factors that tend to distort the fluid composition of the body are 

 not only those imposed by disease, noxious substances and injuries. 

 The requirements of the organism for a continual replenishment of its 

 own material substance demands the ingestion of foodstuffs, minerals, 

 and water itself. It would be an unenviable kind of existence if these 

 had to be ingested at such slow rates that no significant changes 

 occurred in the composition of the fluids both within and without the 

 cells. It is common knowledge that we can ingest at one time consider- 

 able portions of our daily requirements of food, minerals, and water 

 without more than temporary dislocations in the composition of our 

 internal environment, so efficient are the bodily mechanisms that main- 

 tain this composition. 



In addition to this capacity to assimilate at one time considerable 

 quantities of the necessities of life, the higher organisms also possess 

 means to support the level of certain essential constituents of the body 

 fluids at a time when none is being supplied from without. In the ab- 

 sence of such a function all the higher forms of life would have had 

 to remain in close proximity to an ever present food supply and this 

 would have greatly limited the colonization of the land and the possi- 

 bility of further evolutionary processes. 



The vast amount of work carried out in the last fifty years on the 

 function of the endocrine glands has not only served to give an insight 

 into their individual mode of operation but has brought an increasing 

 consciousness of the fact that they act not as independent units but as 

 a correlated and integrated system that is closely associated with the 

 capacity of the organism to adapt itself to the varying conditions of 

 existence. 



Thus we find that the endocrine glands not only regulate the metab- 

 olism of the organic and inorganic elements of the body but do so in 



