Disease and Immunity 69 



by their exercise in carrying that load, and they 

 were able to survive much longer under a 

 killing load. When the load was an overload, 

 that overload absorbed part of the powers they 

 had originally, and they died more quickly when 

 placed in the killing solution. 



In sexual reproduction, two germ cells unite 

 and afterwards develop into a new individual 

 by growth and repeated divisions. This union 

 of cells and subsequent growth and division is a 

 dynamic process which calls for greater or less 

 exertions on the part of the cells involved. If 

 the two germs cells which unite come from 

 parents of the same breed, these cells are much 

 alike and can unite and subsequently divide with 

 a minimum of effort. If they come from differ- 

 ent breeds, then these germ cells are somewhat 

 unlike and it requires greater efforts on their 

 part to successfully fit themselves together and 

 then divide into new cells which constitute 

 proper divisions of the united differences. If 

 they come from different species or different 

 genera, then the uniting cells are still more un- 

 like, and this increased unlikeness calls for still 



