GROWTH AND STRUCTURE OF HYPOPHYSIS IN RAT 355 



to 26-28 per cent of the cell volume in the young held at mainte- 

 nance, and to 23-26 per cent in adults with clu'onic or acute 

 inanition. 



7. According to data obtained by the volumetric method, the 

 (calculated) average diameter of the parenchyma cells of the 

 anterior lobe increases from 10.1 yu in the normal newborn to 

 11.9 yu at three weeks and 13.6 /x at ten weeks (adult condition). 

 In young rats held at maintenance, the average cell diameter is 

 reduced to 9.7-10.2 m; in starved adults to 10.8-11.0 m- The 

 nuclear diameter averages 5.9 fx in the normal newborn, 5.8 m 

 at three weeks, and 6.0 ^ at ten weeks. In the young rats at 

 maintenance the nuclear diameter is reduced to 4.9-5.3 /j.; in 

 starved adults to 5.3-5.5 /x. Direct measurements by another 

 method (with filar micrometer) gave similar results for the 

 nuclear diameters, including also those of the pars intermedia.. 



8. The nurrrber of mitoses in an entire section of the gland is 

 quite variable. Amitosis was never observed. In the normal 

 newborn pars nervosa, the average nmnber of mitoses is 7 per 

 section; at seven days they are rare, and none occur later. In 

 the pars intermedia, the average nmnber decreases from 9 per 

 section in the newborn to about 1 at three weeks; at ten weeks 

 and later they are rare. In the normal pars anterior the rate 

 likewise decreases, being about 62 at birth, 18 at one week, 

 7 at three weeks, 2 at ten weeks, and rare in adults. 



9. In young rats held at maintenance from three to ten weeks 

 of age, mitosis has nearly ceased. No mitoses were found in the 

 partes nervosa and intermedia, although in the pars anterior 

 they still occur occasionally, even in rats nearly dead from 

 inanition. No mitoses were observed in the starved adults. 



10. In the young rats refed after the maintenance period, 

 mitoses reappear promptly in the pars anterior, the average 

 number per section being about 2 after one-half week of refeed- 

 ing, 7 after one week to two weeks, decreasing to an average of 

 3 after four weeks of refeeding. Mitoses were observed but 

 rarely in the pars intei'nredia, and never in the pars nervosa. 

 The rate of mitosis in the hypophysis of the refed rats therefore 



