386 HELEN DEAN KING 



males to 100 females. Apparently, therefore, in the albino rat, 

 as in man and various other mammals, there is normally a nearly 

 equal proportion of the sexes among the young, although in all 

 species there seems to be a slight excess of males. 



THE EFFECTS OF SEMI-SPAYING ON THE SEX RATIO OF THE 



ALBINO RAT 



Six females, belonging to two litters born in October, 1909, 

 were operated upon when they were 16 days old. From three of 

 these females the right ovary was removed, and from the remain- 

 ing three the left ovary was taken. Two of these females, one 

 spayed on the right side and the other spayed on the left side, 

 never had a litter although they were paired with normal males 

 for five months: both of these rats died of pneumonia when they 

 were about nine months old. When dissected each female was 

 found to have but one ovary which appeared normal in every 

 respect. The only reason that can be suggested for the failure 

 of these rats to breed is that they had been attacked by pneu- 

 monia when they were immature and therefore were never in a 

 physical condition to bear young. There is evidence that rats 

 may suffer from pneumonia, in an incipient form, for a consider- 

 able length of time with no manifestations of the disease other 

 than a loss of weight and a failure to breed; and it is only when 

 this disease has nearly run its course that the characteristic 

 difficulty in breathing, which indicates the formation of pus 

 nodules in the lung tissue, becomes at all noticeable. 



Table 1 gives a summary of the number of young produced by 

 the four semi-spayed rats when they had been mated with normal 

 males. The letter R or L after the number given the rat indi- 

 cates that the right or the left ovary had been removed. 



Each litter of every female contained young of both sexes; 

 and although there were more females than males in the total 

 number of individuals that were produced, the excess of females 

 was too small to be considered as significant. The two females 

 spayed on the right side had a total of five litters which contained 

 22 individuals; nine of these were males and thirteen were females. 



