344 READINGS IN EVOLUtlON, GENETICS, AND EUGENICS 



facts learned from a study of precipitins and of anaphylaxis that each 

 species of animal has a thread of fundamental similarity underlying 

 the proteins of all its tissues. There is no reason to suppose that germi- 

 nal tissue forms an exception. The further fact that homologous 

 tissues, though existing in different species of animals, possess similar 

 chemical characteristics, shows that to get an effect there need not 

 be absolute chemical identity between the substance of such a tissue 

 as the lens and the germinal constituents of which it is the expres- 

 sion. And if this is true for lens, why not for other tissues ? 



The blood-serum of any organism with blood thus affords a means 

 of conveying the effects of changes in a parental organ to the germ- 

 cell which contains the antecedent of such an organ. As long as there 

 is little change in the somatic element its germinal correlative would 

 presumably remain constant, but any alternations of the soma which 

 give rise to the formation of anti-bodies or other active agents, par- 

 ticularly if long continued, might induce changes in the germ. Such a 

 h}^othesis would seem to be plausible at least in accounting for 

 degenerative changes such as the deterioration of eyes in such forms 

 as the mole, or in fact, in the formation of vestigial organs in general. 



On the other hand, there is no reason to infer that changes induced 

 in the blood-serum may not also be instrumental in leading to pro- 

 gressive as well as regressive evolution. If we may have germinally 

 destructive constituents engendered in the blood there is no valid 

 reason for supposing that we may not also have constructive ones. 

 When we learn more about what initiates and promotes growth in a part 

 through exercise, or what causes hypertrophy of an organ, we may 

 likewise find how corresponding germinal antecedents of that part 

 may be enhanced. Until such time we shall probably remain in the 

 dark regarding the mechanism of progressive germinal changes. As 

 already indicated, in the hormones and chalones we have a wonderful 

 series of secretions normally circulating in the blood and maintaining 

 general physiological equilibrium. That reciprocal stimulations of 

 various organs occur by this means is a well-established fact. Hyper- 

 trophy or atrophy of an endocrine gland may produce pronounced 

 effects in the furthermost reaches of the body. Again we may inquire, 

 is it reasonable to suppose that the germinal tissues will be inviolate 

 to all this ebb and flow of chemical influence ? Should we not expect 

 specific reactions or selections here no less surely than in other tissues ? 

 Destruction of the pars buccalis of the hypophysis in the frog-tadpole 

 will cause profound alteration in other endocrine organs such as the 



