GROWTH AND STRUCTURE OF HYPOPHYSIS IN RAT 335 



made at later stages. Some allowance must also be made for 

 variations, both in different individuals and in different parts of 

 the gland in the same individual. 



In 2 of the 3 young rats held at maintenance, in which the 

 volumetric data were obtained, there appears to be a relative 

 increase in the nuclear volume to 25.9 per cent and 28.4 per cent 

 respectively'. This involves a corresponding loss in relative vol- 

 ume for the cytoplasm, which is doubtless typical (fig. 3). Indi- 

 vidual variations occui", however, as in the third case (S 6.23, 

 which also had a small stroma volume), in which the nuiclei 

 formed 23.4 per cent by volume, or slightly less than the normal 

 at three weeks. 



In the two older rats subjected to chronic and acute inanition 

 the relative increase in nuclear volmne (with corresponding cyto- 

 plasm decrease) appears even more strongly marked, reaching 



23.1 and 25.7 per cent respectively, in comparison with 19.7 per 

 cent for the normal. The crowding of the nuclei with reduction 

 of cytoplasm is evident in figure 5. Allowance must of course 

 be made for variations, but the general tendency is unmistakable. 



c. Estimated size of cells and nuclei 



The average diameters of the cells and nuclei of the paren- 

 chyma in the pars anterior, calculated as explained under ''Mate- 

 rial and Methods," are given in the last two columns of table 3. 

 The average cell diameters by this method appear to increase 

 from 10.1 yu in the newborn to 11.9 /x at three weeks and 13.6 n 

 at ten weeks (sixty-seven days). This appears to represent the 

 average permanent adult size, although individual variations 

 occur. 



In the young rats held at maintenance, the average cell diame- 

 ters in the three cases measured by this method range from 9.7 /x 



10.2 fi, or considerably less than the normal at three weeks (11 .9 /j.) . 

 In the adults subjected to acute and chronic inanition, the cell 

 diameters are 10.8 fi and 11.0 yu, likewise a marked reduction in 

 comparison with the normal (13.6 ^i). 



The corresponding average nuclear diameters, estimated by 

 this method, show very little change with age in the normal rats. 



