94 GENETICS 



ever, is not the inheritance of an acquired character 

 or of a definite somatic modification. 



When a man of the present generation has rheu- 

 matic gout, it is a severe stretch both of patriotism 

 and of the powers of heredity to trace the origin of 

 the affliction back to a revolutionary ancestor who 

 acquired sciatic rheumatism by sleeping on the 

 ground at Valley Forge, yet this is quite as direct as 

 many alleged instances of the inheritance of disease. 



In the majority of instances, apparent cases of 

 disease inheritance are merely instances of reinfec- 

 tion. This reinfection of the offspring may occur 

 very early in embryonic life, or it may happen after 

 birth, provided the offspring are exposed to the same 

 environment as that in which the parent acquired the 

 disease, but in any case reinfection is not heredity. 



13. THE GERMPLASM THEORY SUFFICIENT TO AC- 

 COUNT FOR THE FACTS OF HEREDITY 



Weismann holds that the theory of the continuity 

 of the germplasm, already considered in a previous 

 chapter, is sufficient in itself to account for the facts of 

 heredity. Hence it is quite unnecessary to fall back 

 upon the inheritance of acquired characters as an ex- 

 planation, since this theory is at least difficult, if not 

 impossible, of satisfactory proof. 



To prove the inheritance of acquired characters, 

 according to Weismann three things are necessary : 

 first, a particular somatic character must be called 

 forth by a known external cause ; second, it must be 

 something new or different from what was already 



