66 



Scientific Proceedings (56). 



for the spayed animals, was found to be 12.74 m S-> a °d for the 

 normals 13.49 mg. — a variation no larger than would probably 

 be found among two groups of normal rabbits. 



Several objections might be made to the above experiment: 

 (1) the ages of the animals were uncertain, (2) it was not known 

 whether the females had ever been pregnant, (3) the castrated 

 and control animals were not necessarily of the same litter. For 

 this reason another investigation was undertaken on a second 

 series of rabbits. 



In the second experiment most of the operated and control 

 animals were selected from the same litter. It was known that, 

 with a few exceptions, the females had never been pregnant. The 

 animals were also younger than those of the first series, many 

 weighing less than one kilo. The sexes were separated and kept 

 under the same conditions as in the first experiment. At the end 

 of about four months after operation a control and an operated 

 animal were killed by coal gas on the same day, the reduced body 

 weight recorded, and the pituitaries removed and weighed as 

 before. 



In the male group there were ten animals which could be 

 controlled by eight of the same litter. The average weight of 

 these pituitaries in milligrams per kilo of body weight is for the 

 castrated 15.3 mg. and for the controls 15.8 mg., which shows a 

 difference so small that it is entirely negligible. Among the 

 females six were controlled by five of the same litter and in this 

 case the average for the spayed animals is 16.49 mg. and in the 

 controls 13.27 mg. or an increase of about 24 per cent, by this 

 grouping. 



It is significant to note that the curves of growth plotted from 

 the weights taken each week show a distinct gain of the operated 

 over the control animals in case of the males but not in case of the 

 females, thus agreeing with Hatai's 1 ('13) results from the albino 

 rat in that when castration is followed by an overgrowth in body 

 weight there is no increase in the weight of the pituitary. The 

 average for the whole series of twenty castrated males was found 

 to be 15.94 m g-i while the seventeen controls gave an average of 

 14.38 mg., thus showing a gain by the castrated males of less than 



1 Hatai, Journal of Experimental Zoology, Vol. 15, p. 297, 1913. 



