GROWTH AND STRUCTURE OF HYPOPHYSIS IN RAT 341 



TABLE 5— Concluded 



NUMBER OP MITOSES COUNTED IN ENTIRE CORONAL 

 SECTIONS OF THE HYPOPHYSIS IN THE 



Pars anterior 



Para 

 intermedia 



Pars 

 nervosa 



C 3. Rdls rcfcd ttco weeks after maintenance from three to twelve weeks of age 



C 4- Rats refed four weeks after maintenance from three to twelve weeks of age 



C 5. Rat refed six months after maintenance from three to twenty weeks of age 



S 33.118 m 346 229.0 ' 0.0094 











a. During normal growth of the hypophysis 



To determine the rate of mitosis in the normal gland at vari- 

 ous ages, sections were examined from 14 individuals, varying 

 from newborn to 225 days of age (tables 5 and 6). In the new- 

 born, mitosis is very active throughout the gland, the average 

 being 62 mitoses in each section for the pars anterior, 9 for the 

 pars intermedia, and 7 for the pars nervosa. Considering the 

 difference in the areas of the three lobes (fig. 1), it may be con- 

 cluded that the actual number of mitoses for a given nmiiber 

 of cells (the 'mitotic index' of Minot) would probably be similar 

 in all three lobes, though somewhat less in the pars nervosa. 



In the pars nervosa, mitoses soon disappear. From an average 

 of 7 per section in the newborn, they decrease to an average of 

 two-fifths (i.e. 2 mitoses found in 5 sections) at seven days. In 

 later stages (twelve days and above) none was found in any 



