74 Proceedings of the Royal Physical Society. 



quote the following passages : — ''Through what agency is the 

 environment enabled to act on the germ plasm ? To me the 

 only conceivable one is a chemical influence, through pro- 

 ducts of metabolism and specific internal secretions. We 

 have seen in a previous chapter that the products of 

 metabolism of an organism may exert a retarding influence 

 on its own growth, and in some cases a stimulating effect 

 on the growth of other organisms. Physiological research 

 of the last few years has shown that most of the organs and 

 tissues of the body have specific internal secretions, which, 

 passing into the general circulation, may exert an influence 

 of vital importance on the general metabolism of the organism. 

 Thus extirpation of the thyroid gland produces symptoms 

 which in many animals end fatally, but which may be 

 diminished or suppressed by feeding on the gland substance, 

 or injection of extracts of it. Extirpation of the suprarenal 

 glands results in much more speedy death, and here again 

 the injection of extracts may delay the fatal issue." 



Dr Vernon gives several other examples, and then goes on 

 to say : — " Does it not seem distinctly probable, therefore, 

 that every tissue in the body to some extent affects every 

 other tissue ? Each may have its own specific products of 

 metabolism, and perhaps specific internal secretions, which, 

 passing into the general circulation, may in turn stimulate 

 or depress, or otherwise affect, every other tissue in the body. 

 Whenever a change in the environment acts upon the 

 organism, therefore, it to some extent affects the normal 

 excretions and secretions of some or all of the various tissues, 

 and these react not only on the tissues themselves, but also 

 to a lesser degree upon the determinants representing them 

 in the germ plasm." 



This " specific secretion hypothesis," as it is termed by Dr 

 Vernon, has a striking resemblance to the hypothesis put 

 forward in this paper. It differs, however, in his basing his 

 hypothesis on Weismann's determinants. He also gives 

 no recognition to the suppression of one set of the dual 

 characters in the tissue cells, which is necessarily the founda- 

 tion of the hypothesis here put forward. In conclusion, I 

 may say that if the hypothesis of Driesch, that the nucleus 



