THE ORIGIN OF THE HORMONES 15 



THE ORIGIN OF THE HORMONES. 



The internal secretions may also be classified according to 

 their origin. The distinction is between (a) products of the 

 chemistry of the organs which are simply the end-products of 

 decomposition, i.e., the waste or by-products of the process of meta- 

 bolism ; and (b) substances which are the outcome of a synthetic 

 process. It would be wrong, however, to imagine that the true 

 hormones are all included in the latter group. For, in many 

 instances, it is just the products of decomposition formed during 

 cell-activity which are the stimulating agents, by whose aid the 

 function, not of the cells only, but of other tissues, is promoted 

 and maintained. 



That form of activity which is usually ascribed to automatic 

 irritation of the nervous centre, is not really automatic; it is in 

 reality brought about by the agency of the products of cell- 

 metabolism and by the vital processes of the protoplasm. Thus, 

 in suffocation, the changes in the respiratory and cardiac activity, 

 the spasms of the voluntary muscles, and the tonic contractions 

 of the muscular tissue of the vessels, are due solely to over- 

 irritation by the products of decomposition, an excessive quantity 

 of which is circulating in the blood. The regulation of normal 

 respiration, moreover, is due to the agency of chemical stimuli. 

 Nervous irritation coming from the periphery is able to modify 

 respiration, but is unable to regulate it. It is more probable that 

 the so-called automatic irritation of the centre of respiration, is 

 brought about by the effete products, formed during and by the 

 activity of the tissues. According to Miescher, and there is good 

 grounds for his view, the actual agent is carbonic acid (CO 2 ), 

 one of the end-products of oxidation. The fluctuating quantity 

 of CO 2 in the blood brings about changes in the respiration and 

 in the supply of oxygen, which are entirely suited to the momen- 

 tary needs of the organism. If the amount of CO 2 in the blood 

 increases, the need of the tissues for oxygen is satisfied by means 

 of deeper and accelerated respiration. It is possible that, where 

 the activity of the tissues is excessive, especially in the case of 

 muscular exertion, the breathing apparatus is influenced by other 

 acid products of incomplete combustion, as lactic acid (Geppert 

 and Zuntz). But in normal respiration, the disassimilatory hor- 

 mone is carbonic acid, the common product of protoplasm. It 

 must, however, be remembered that, in the opinion of many, the 

 essential factor in the regulation of normal respiration is not the 

 accumulation of carbonic acid, but the lack of oxygen. It may 

 be a combination of both. 



This example it is not the only one but it is the best known 

 goes to show that the end-products of metabolism play an 

 important part in the accomplishment of chemical correlations. 



