190 THE STORY OF LIFE'S MECHANISM. 



two quite different views among biologists ; and, 

 while it is not our purpose to deal with disputed 

 points, these views are so essential to our subject 

 that they must be briefly referred to. One class 

 of biologists adheres closely to the view already 

 outlined, and insists for this reason that acquired 

 variations can not under any conditions be in- 

 herited. They insist that all inherited variations 

 are congenital, and due therefore to direct varia- 

 tions in the germ plasm, and that all instances of 

 seeming inheritance of acquired variations are 

 capable of other explanation. The other school 

 is equally insistent that there are abundant in- 

 stances of the inheritance of acquired characters, 

 claiming that these proofs are so strong as to 

 demand their acceptance. Hence this class of 

 biologists insists that the explanation of heredity 

 given as a simple handing down from generation 

 to generation of a germ plasm is not complete, 

 and that while it is doubtless the foundation 

 of heredity, it must be modified in some way 

 so as to admit of the inheritance of acquired 

 characters. 



There is no question that has excited such a 

 wide interest in the biological world during the 

 last fifteen years as this one of the inheritance of 

 acquired characters. Until about 1884 the ques- 

 tion was not seriously raised. Heredity was 

 known to be a fact, and it was believed that 

 while congenital characters are more commonly 

 inherited, acquired characters may also frequently 

 be handed down from generation to generation. 

 The facts which we have noted of the continu- 

 ity of germ plasm have during the last fifteen 



