134 ON VARIABILITY AND ADAPTATION 



have not burst the bottles, have led them to assume most grotesque 

 shapes. In fact there has been developed such a muddle that no 

 amount of midnight oil and wet cloths bound around the temples 

 permit the ordinary mortal to disentangle and follow the course 

 of one theory. 



This being the state of affairs, it is little wonder that we 

 have been unwilling to apply the theories of the biologists 

 to the problems of medicine, and this all the more because 

 the trend of these theories has been in apparently strong 

 opposition to medical experience. Of all the workers of late 

 years Weismann has had the most influence upon biological 

 thought, and his theory, if not accepted by all in its 

 entirety — and if, indeed, now found unacceptable, — has, never- 

 theless, profoundly affected the general consideration of this 

 subject of heredity. That theory is very complicated, and with 

 Weismann's successive publications has not by any means become 

 easier to follow or epitomize in language devoid of technicalities. 

 Still, if not every schoolboy, at least every educated man is 

 supposed to comprehend the general tenor thereof and its main 

 thesis or conclusion, that acquired characters — characters ac- 

 quired by the individual — are not and cannot be transmitted to 

 the offspring. To use Weismann's own expression, " We main- 

 tain that somatogenic characters (characters originating in the 

 cells and tissues of the body) are not transmitted, or rather, that 

 those who assert that they can be transmitted must furnish the 

 requisite proof. The somatogenic characters not only include 

 the effects of mutilation, but the changes which follow from 

 increased or diminished performance of function, and those which 

 are directly due to nutrition and any of the external influences 

 which act upon the body. Among the blastogenic characters 

 (characters originating in connexion with the germ cells), we 

 include not only all the changes produced by natural selection 

 operating upon variations in the germ, but all other characters 

 which result from this latter cause." 1 In natural selection is to 

 be found the key of the phenomena of inheritance. 



Now, up to a certain point, we as medical men are prepared 

 to accept this teaching. We know from experience that acquired 

 mutilations are not transmitted ; we acknowledge that no clear 



1 Weismann, On Heredity. Authorized translation by Poulton, Schonland, 

 and Shipley, Oxford, 1889, p. 413. 



