304 THE AMERICAN NATURALIST [Vol.LVI 



ters in the presence of alcohol along purely physiological 

 lines would be a simple matter, but a genetic explanation 

 appears to be required when it comes to the increase over 

 the controls given by untreated descendants of treated 

 animals. No general depression or stimulation will ac- 

 count for the continuation of small litters together with 

 the increase in number of litters in the generations not 

 given alcohol directly. It seems necessary to assume that 

 there are genetic factors influencing the number of litters ; 

 alcohol prevents the reproduction of such females as carry 

 factors working in the direction of lower reproductive ca- 

 pacity, so that the litters come alone from females carry- 

 ing higher litter-producing capacity ; the next generation 

 will produce higher numbers of litters than the unselected 

 controls, for the controls still carry all grades of fertility, 

 while the tests lack the genetically lower grades. The 

 treated offspring of treated rats produced fewer litters 

 than their controls, but genetically they were superior, 

 as shown by untreated offspring giving more litters than 

 their controls ; they were superior to the first generation, 

 for, instead of a 65 per cent, reduction, they gave only 

 a 35 per cent, reduction in the number of their litters. 

 Whereas the immediate presence of alcohol reduces the 

 number of litters, it acts to increase the number in the 

 next generation; therefore alcohol may produce two re- 

 sults upon a single character in two generations. This 

 could lead to much confusion were it not so easy to un- 

 derstand the first result as the cause of the second. 



This selective action of alcohol will account for the re- 

 sults from the number of litters, but will not account for 

 the uniform results given by litter size. If this is a 

 correct statement of the situation, it indicates that the 

 number of litters is influenced by genetic factors that are 

 not identical with those influencing litter size. Although 

 such a distinction between genetic bases for the numbers 

 of litters and litter size has apparently not been made, 

 it is not difficult to conceive, for litter size is largely 

 dependent upon the number and constitution of the germ 



