1905.] the Interstitial Cells of the Ovary in the Rabbit. 49 



Taking the radius of the cells it is seen that the increase in its length in the 

 cell during pregnancy is from 8"5 to 16 - 3 or very nearly double. 



If the volume of the sphere be taken as ^ ir . r 3 and the cell be taken as a 

 sphere, the ratio of the non-pregnant cell to the cell at the maximum size 

 attained during pregnancy becomes almost exactly 1 : 7, which would allow 

 sufficient enlargement of the ovary to account fully for the increase in size. 

 It is not to be supposed that all the cells enlarge to the same extent, but it 

 may reasonably be supposed that they enlarge to about five times their 

 normal size. This will account for the enlargement of the whole ovary, and 

 there would seem therefore to be no necessity to seek any further cause of 

 the enlargement of the ovary during pregnancy. 



The only other possible cause which suggests itself at once is of course the 

 division of cells, but although I have examined some hundreds of sections of 

 pregnant ovaries, I have not found any trace of this happening. In giving 

 the above figures I do not wish to suggest that the measurements are 

 absolute. They are subject most probably to individual variations, depending 

 possibly upon the number of foetuses in each pregnancy, and on various 

 other circumstances. The ovaries in question were, however, taken quite 

 haphazard in regard to all external causes, which allows some scope for 

 differences in the ovary, and the results are fairly definite. They show a 

 great increase in the size of the ovarian interstitial cells during pregnancy, 

 and that the main increase is reached by about the twenty-second day, and is 

 sustained until just before birth, when there is a slight diminution in size. 



In this connection there is one feature to be dealt with, namely, the shape 

 of the cell. Up to about the twenty-fourth or twenty-fifth day it is not 

 difficult to find approximately spherical cells to measure. After this period, 

 however, the difficulty of doing so becomes very great, if not impossible. 

 The cells are angular and seem crushed together, and I would suggest that 

 possibly the cells may be really still undergoing slight increase in size, but 

 that the capsule having almost reached its maximum stretching capacity does 

 not admit of the desired expansion, and the cells instead of being spherical 

 become more closely packed in order to find room for the additional bulk, 

 filling in as it were the interstices rather than causing an increase in size in 

 the spherical direction. 



The rounded appearance is resumed very shortly after birth, and there is 

 also a slight decrease in size. Why there should be a decrease before birth 

 is a point upon which I feel it is impossible to offer any suggestion. The 

 mechanism of the production of labour is a question upon which very little 

 is definitely known ; if, however, it be the function of the ovary to cause the 

 adhesion of the fcetus to the uterine wall (Fraenckel), a function carried out 



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