GROWTH AND STRUCTURE OF HYPOPHYSIS IN RAT 327 



(liaineter will froqiiontly lie outside the optical plane chosen. 

 On account of the unavoidable spherical aberration, a larger 

 field will be available in a single optical plane if the section is 

 a little thicker, hence 5 m is preferable to 3 n for this purpose. 



Four different fields from typical regions were thus drawn in 

 each case, and the average results taken (table 3), The total 

 number of nuclei in the four fields varied from 269 (in 8t 47.5) 

 to 509 (in S 6.23). If we assume that the nuclei are spherical 

 (which is, of course, not strictly true), the average area per 

 nucleus in a given optical plane should, according to the rules 

 of solid geometry, represent two-thirds the area of the corre- 

 sponding great circle. (The volume of a sphere equals two- 

 thirds of the volume of the circumscribed cylinder.) Upon this 

 assumption, the average nuclear diameter was calculated (table 

 3). The corresponding average cell diameter was also calculated, 

 assuming that the cytoplasm surrounds the nucleus in a layer 

 of uniform thickness. 



The diameters of nuclei and cells thus calculated can of course 

 be considered only as roughly approximate. So far as the nuclei 

 are concerned, however, the results were controlled by a series 

 of direct measurements (with a filar wheel-micrometer eyepiece) . 

 In this case, the measurements were not restricted to a single 

 optical plane, but the maximum nuclear diameters were obtained 

 by focussing. The average nuclear diameters thus measured are 

 given in table 4. Some variability is naturally to be expected, 

 but the results by the two independent methods are seen to be 

 in fair agreement. 



RELATIVE VOLUMES OF THE PARTS (LOBES) 



a. Normal growth 



It will be noted in table 2 that the 'volume of lobes' is usually 

 slightly less than the corresponding 'volume of gland.' The dif- 

 ference represents the volume of the hypophyseal cavity. This 

 is relatively small (fig. 1), rarely exceeding 3 per cent of the total 

 volimie, and is not appreciably affected by inanition. Since 

 the hypophysis was removed by division of the infundibulum, 



