PHYSIOLOGICAL PROPERTIES OF THE GONADS. 29! 



In reference to growth curves, as well as to all other elements 

 of the investigation, three particular points have been kept in 

 mind: (i) the possible demonstration of sexual differences, (2) 

 the effects conditioned by total castration, and (3) the effects con- 

 ditioned by total spaying. 



Sexual Differences. Comparing the growth curves of the nor- 

 mal animals, male with female (Fig. i), one sees that the males 

 are constantly the heavier up to the end of the first year of growth, 

 when the average weight of the two groups is the same. This 

 agrees with the findings of Minot ('91), who demonstrated that 

 the male guinea pigs were heavier than the females (as a group) 

 up to about the end of the first year, after which the female 

 growth curve crossed that of the males, and from this time on the 

 females were from i per cent, to 7 per cent, heavier than the males. 



Total Castration. From a glance at the growth curves in Fig. i, 

 or reference to the average weights from both groups of animals 

 as seen in Table I., it becomes apparent that castrated males are 

 lighter in weight than normal males at all ages from ninety days 

 to the end of one year. In other words, castration causes a rela- 

 tive loss in weight in the guinea pig when compared with the 

 normal male. 



Total Spaying. Spayed females also exhibit a relative loss in 

 weight when compared with the normal females. The young 

 spayed females at the beginning of the experiment were slightly 

 heavier than the normal females, due merely to chance variation 

 in weight in the selection of the animals, but at the age of ninety 

 days the normal females are slightly heavier and continue so 

 throughout the experiment until the 36oth day, when the spayed 

 females averaged approximately i per cent, heavier than the nor- 

 mal females. One is forced to conclude from this data that spay- 

 ing results, for a certain period, in a decreased body weight (com- 

 pared with the normal females), -but that this loss is made good 

 at a later time. 



Discussion. The particular point in mind for solution was 

 whether the weight of an animal could be depended upon to offer 

 an index of its sexual condition in case of sex-gland transplanta- 

 tions. As mentioned above, Steinach has placed considerable 

 emphasis on the differences in weight after castration and spaying 



