UTILISATION OF PROTEIDS IN THE ANIMAL 171 



the cell, and that a process of hydrolysis, due to their action, 

 precedes or accompanies other changes in the proteids when 

 tissue breakdown is, for any reason, determined. It must be 

 clearly understood, however, that if the cell extracts energy from 

 its own proteid, as proteid, the hydrolytic breakdown in question 

 is incapable of yielding this energy, which must be extracted 

 upon different lines, or arise from other changes accompanying 

 or succeeding hydrolysis. It may well be believed that the 

 products of autolysis suffer the same fate during utilisation 

 as that suffered by amino-acids arriving from the bowel, 

 since their nature is similar. 



Indeed, there is one interesting aspect of metabolism which 

 the recognition of the existence of intracellular ferments has 

 undoubtedly illuminated — that constituted by the events ol 

 starvation. It is well known that the wasting which occurs 

 in the absence of food falls but little upon organs the functions 

 of which are absolutely necessary to the carrying on of life. 

 Thus the heart and nervous system may lose but 3 per cent, 

 of their weight when the muscles lose over 30 per cent. Since 

 autolysis normally yields products similar to those formed from 

 foodstuffs in the intestine, we realise that autolysis of the less 

 necessary tissues may, in hunger, maintain uniform conditions of 

 nutrition for the more necessary tissues [Leathes]. This would 

 hold, not only as regards the maintenance of structural integrity, 

 as in the case, say, of the heart ; but also in the maintenance 

 of the supply of nitrogenous precursors of secretions essential 

 to life, as in the case of, say, the activities of the adrenal gland. 

 This last instance will repay some closer attention. The body 

 exhibits in a very striking way a correlation of function by 

 chemical means. The normal course of activity in any one 

 organ or tissue may be wholly dependent upon the circulation 

 of chemical substances prepared specifically by quite other 

 organs or tissues. The substances concerned in these phe- 

 nomena — " chemical messengers which, speeding from cell to 

 cell along the blood stream . . . co-ordinate the activities and 

 growth of different parts of the body" — have been called 

 "hormones" by Prof. Starling. Among these hormones is one 

 (adrenaline), prepared by the suprarenal glands, the circulation 

 of which is absolutely essential to the maintenance of normal 

 blood-pressure and the visceral functions. 



Now adrenaline happens to be the only hormone of known 



