320 C. M. JACKSON 



The nuclei, generally speaking, appear somewhat more re- 

 sistant to inanition than does the cytoplasm. In form and size, 

 there appears to be comparatively little change in man}" of the 

 thyroid nuclei in rats held at maintenance from 3 to 10 weeks of 

 age. The average diameter found in the nucleus of the more 

 nearly cubical cells is between 5 and 6 micra, while the normal 

 at corresponding age is only about 6 micra. It is therefore evi- 

 dent that the nuclear decrease in volume is relatively small. (A 

 decrease of even 10 per cent in the nuclear diameter would cor- 

 respond to a loss of about 27 per cent in volume, however.) In 

 the more flattened cells (which, as we have seen, usually include 

 the majority), the nucleus is also usually correspondingly flat- 

 tened, with some loss in volume. Even in the flattened cells, 

 however, the nuclear loss is apparently relatively much less than 

 the cytoplasmic loss in volume. 



Although the loss in volume of the nucleus in the thyroid of 

 maintenance rats is relatively small, the structure is usually dis- 

 tinctly modified. Nuclei of the typical normal appearance (as 

 in fig. 2) are rare. The modifications found are varied, but may 

 be classified in two groups — hypochromatic and hyperchromatic. 



The hypochromatic type is comparatively rare. In 14 cases 

 of maintenance rats, it appeared extensively but once (shown in 

 fig. 7), and in 3 other cases more or less frequently in scattered 

 cells. The hypochromatic nuclei (fig. 7) usually appear normal 

 in size, or even slightly swollen. They are very light and vesic- 

 ular in ap]:)earance. The nuclear membrane is thin, but sharp 

 and clear; the nuclear network and granules faint and indistinct. 

 The interior of the nucleus is filled with a clear nuclear sap 

 (karyolymph), which is nearly colorless, or with a very pale blue 

 homogeneous tint. In exceptional cases these hypochromatic 

 nuclei apparently undergo complete karyolysis, and disappear 

 without preceding change in form or size. 



The hyperchromatic form of nucleus on the other hand, is 

 typical. In the 14 cases of maintenance rats, it appeared more 

 or less extensively in thyroid of all (even in the one case in which 

 the hypochromatic type predominated). Apparently the earli- 



