EFFECT OF CASTRATION ON THE WHITE RAT 307 



litter and thus making comparisons within the litter. This is 

 certainly the safer method in determining any alterations follow- 

 ing an operation. When this method is not available, a consider- 

 able number of animals both for control and for operation must 

 be examined in order to determine the extent of variation shown 

 by the two groups. 



A search through the literature reveals the fact that such a 

 method as that mentioned above has not been used by most inves- 

 tigators, and thus the conclusions have been drawn mainly from 

 a few operated animals contrasted with even a less number of 

 controls, which in turn did not certainly belong to either the litter 

 or the strain of the operated animals themselves. These facts 

 throw doubt on the correctness of the results thus obtained and 

 indeed the recent work of Marrassini and Luciani ('11) who 

 worked with great care and who, contrary to the previous investi- 

 gators, find no enlargement of the hypophysis in either guinea 

 pigs or rabbits, accentuate these doubts more strongly. 



SEMI-SPAYED RATS 



The present series contains 12 litters comprising 21 semi-spayed 

 and 20 controls. The series is divided into four groups, each 

 containing three litters. The result of the observations is given 

 in table 3. 



Body weight. In this series the weight of the body at 280 days 

 in age is given by Stotsenburg ('13) as 140 grams for semi-spayed 

 and 145 grams for controls. At the time of killing (326 days) 

 however, some of the rats had gained in weight, particularly the 

 semi-spayed. As is shown in the table above, a substantial 

 increase in body length and weight of body was made by the semi- 

 spayed over that of the controls after 280 days of age. The differ- 

 ence in body weight, when body length is taken as the basis for 

 the comparison, between the semi-spayed and the control, is 

 insignificant amounting to only —2.65 per cent. 



From this it is concluded that semi-spaying does not modify 

 the normal relation existing between body weight and body length, 

 and consequently a slight overgrowth in body weight shown at 

 the time of examination was not due to an accumulation of fat. 



