EFFECT OF CASTRATION ON THE WHITE RAT 309 



Tail length. Tail length with respect to body length is not 

 modified by semi-spaying. The difference is negligible, amount- 

 ing to 0.67 per cent in favor of the controls. 



Brain weight. Here again the brain weight tends to be small 

 in the semi-spayed to about the same degree as has been noted 

 in the case of the spayed rats; the difference is 0.17 per cent in 

 favor of the controls. 



Spinal cord weight. The weight of the spinal cord of the semi- 

 spayed is a little over 1 per cent below that of the controls. Here 

 also the difference is very small, nevertheless there appears a 

 constant tendency to slight reduction in the operated rats when 

 compared with the unoperated. 



Percentage of ivater in the brain and in the cord. It is clear from 

 the table that the water content in the semi-spayed is practically 

 identical with that of the controls; the difference between the two 

 being 0.13 per cent in the case of the brain and 0.22 per cent in 

 the case of the spinal cord in favor of the controls. 



Consequently we conclude that the water content in the central 

 nervous system is not modified by semi-spaying. 



Weight of hypophysis. The weight of the hypophysis in the 

 operated rats is practically normal to body length, while that of 

 the control rats is considerably heavier than the body length calls 

 for. Furthermore, the normality of all other characters in the 

 semi-spayed rats indicates that the difference of nearly 16 per cent 

 shown by the hypophysis in favor of the control rats is not due 

 to the diminution of this organ in the semispayed, but is rather 

 due to the abnormal size of it in the control rats. Without being 

 able to explain this high value in the controls, I conclude never- 

 theless that the weight of the hypophysis in the operated rats is 

 not modified. 



Weight of ovaries. We note here a beautiful instance of compen- 

 satory growth. The weight of the ovary of one side in the semi- 

 spayed is almost twice the weight of the normal single ovary; 

 the average departure from the double weight being only 7 

 mgms. or — 14 per cent. Exactly what structures are responsible 

 for such a compensatory growth of the ovary still requires to be 

 investigated. 



