420 PROGRESS OF SCIENCE IN THE CENTURY. 



result is readily interpretable as due to cumulative 

 modifications hammered on each successive genera- 

 tion without there being any inheritance of these 

 modifications. It is also possible that the reproduc- 

 tive cells were influenced along with the body or 

 outside of the body by the continuous change of 

 salinity. 



Another typical line of evidence is that based on 

 the study of immunity a subject of great practical 

 importance and theoretical interest. A due discus- 

 sion of it is impossible in our space here, but the par- 

 ticular point admits of being briefly stated. It is 

 well known that negroes and mongolians are rela- 

 tively immune to yellow fever, and it is believed 

 by many that a progressive immunity to various 

 diseases is observable in our own country. Is not 

 this proof positive of the inheritance of an acquired 

 character? The sceptical answer is first of all that 

 the original immunity may have been a congenital 

 peculiarity, which has become dominant in the race 

 by the elimination of those members who were not 

 immune. And if it be objected that there are cases 

 where a mother-rabbit or guinea-pig has been arti- 

 ficially rendered immune to certain diseases, and has 

 had young ones born immune, the answer is again 

 ready, that this was probably due to a kind of infec- 

 tion before birth, some anti-toxin or other having 

 probably passed from the mother to the unborn 

 young.^ 



Indirect Importance of Modifications. That 

 modifications are common, everyone admits; that 

 they are often of great value to the individuals who 

 acquire them is also certain ; the question is whether 

 they are of direct value to the race, seeing that we 

 cannot prove their transmissibility. 



