354 C. M. JACKSON 



SUMMARY 



1. Dui-iiiji; iionnal postnatal growth there is considerable indi- 

 vidual variation in the relative volumes of the three parts (lobes) 

 of the hypophysis; but in general in the older rats the pars ante- 

 rior (distalis) becomes relatively larger, and the pars nervosa 

 correspondingly smaller, the pars intermedia remaining about 

 the same in relative (percentage) volmne, 



2. The relatively larger hypophysis of the female rats is due 

 chiefly (if not entirely) to a larger anterior lobe. 



3. During inanition, the volume-changes in the lobes are vari- 

 able. In young rats held at maintenance (constant body weight) , 

 the pars anterior is somewhat reduced, the intermedia and 

 nervosa correspondingly larger. In chronic (adult) inanition the 

 partes anterior and intermedia appear reduced, the nervosa 

 increased. In acute (adult) inanition, the pars anterior appears 

 relatively increased, intermedia decreased, and nervosa un- 

 changed in relative volume. 



4. In young rats refed one-half week, one week, two weeks 

 and four weeks after maintenance, there is some variability, 

 but in general a gradual return to the normal proportions in 

 the lobes of the hypophysis. After a prolonged period of mainte- 

 nance, however, the relative volume of the lobes may remain 

 permanently abnormal. 



5. In the pars anterior of the normal newborn rat, the vessels 

 and associated stroma form 6.7 per cent by volume, increasing 

 to 9.6 per cent at three weeks, and to 10.6 per cent at ten w^eeks 

 (adult condition). In young animals held at maintenance, the 

 volume of the vascular stroma usually increases to about 13 per 

 cent, and in acute or chronic inanition of adults to about 17 per 

 cent. The parenchyma is, of course, correspondingly reduced 

 in relative volmne. 



6. In the parenchyma of the pars anterior the nuclei form 

 about 34 per cent of the total cell volmne in the newborn, de- 

 creasing to about 24 per cent at three weeks and to 20 per cent 

 at ten weeks (adult relation). The cytoplasm increases corre- 

 spondingly in relative volume. During inanition, the loss is 

 usually greater in the cytoplasm, the nuclei thereby increasing 



