12 INTERNAL SECRETION 



is employed, only that proportion of the active substance which is 

 for the time being in the tissues, and this is doubtless very small, 

 becomes absorbed ; while under natural conditions or after trans- 

 plantation, the increase is almost incalculable because there is 

 constant production. 



In face of the difficulties which beset the theory that the 

 neutralization of toxins takes place within the organ itself, we 

 are forced to assume that there is a relationship between the 

 process of neutralization and that of secretion. The neutralization 

 of the hypothetical toxin is assumed to take place, not within 

 the organ itself, but in the blood-stream and by the agency of a 

 specific antitoxic organic secretion. In that case the function 

 exercised by the organ would not be merely excrementitial (using 

 the word in its special sense), but truly secretory. 



This hypothesis can only hold good where the presence of 

 the supposed toxin on the one hand, and the process of 

 neutralization on the other, can be demonstrated in vitro. As our 

 knowledge of the internal secretions increases, the idea of a 

 process of neutralization of toxins becomes narrowed in its appli- 

 cation and, though to-day it may still be essential to the doctrine 

 as a whole, in course of time it will probably disappear altogether. 



THE ACTIVITY OF THE HORMONES. 



We will now endeavour to classify the internal secretory 

 organs according to the manner in which their secretions act. 

 The secretory products fall readily into two groups. The first 

 of these comprises those secretions which, either from their organic 

 constitution or because they act as sources of energy, assist in 

 the building up or the activity of other organs. These may be 

 called the " nutritive secretions." The second group includes 

 those substances whose sole influence is upon the manner in which 

 the materials and energies, already collected in the organs, are 

 employed. These are the true hormones. 



In addition to the antitoxic and neutralizing substances 

 already described, the first group includes the nutrient or pro- 

 ductive internal secretions. These are the nutritive material of the 

 organs, and they are derived by the chemical agency of the 

 intestinal wall and glands of the appendix, from the foodstuffs. 

 As products of assimilation, they pass into the blood- and lymph- 

 streams and are carried to the different tissues. The albumin, 

 which is absorbed by and circulates in the blood, and the sugar, 

 formed from glycogen by the liver, are instances of such waste- 

 secretions, for they supply the direct material for the renovation 

 and activity of the organs. 



A large number of these substances, however, act also as 

 hormones and exert a modifying influence upon the very 

 processes by which they are changed and consumed. We know, 



