188 Dynamic Evolution 



ted from parents who have acquired it, and 

 that by continual vaccination the race may 

 become immune to small-pox. By repeated 

 small doses Ehrlich produced a race of try- 

 panosomes which were immune to trypan 

 red, and this resistance was transmitted 

 through many generations. 



Germ cells begin to multiply by segmenta- 

 tion at the time of puberty, and the rate at 

 which they multiply corresponds more or 

 less to the rate at which the ordinary body 

 cells multiply. They increase very rapidly 

 soon after puberty, but the rate of increase 

 gradually declines and finally ceases in very 

 old persons. We see the result of this in the 

 fact that animals are more prolific when 

 young than when old. In man we see this in 

 the fact that the greatest number of children 

 are born when their fathers are 30 years of 

 age, and this in spite of the fact that some 

 men do not marry until after that age. 



From what has been stated before, the 

 natural deduction from these facts is that 

 fecundity should be greater in the offspring 



