MESENCHYME CELLS OF TISSUE CULTUEES 437 



CHANGES IN THE NUCLEUS 



Normally, the outline of the nucleus can usually be deter- 

 mined by the structures within the surrounding cytoplasm. 

 Within a minute or more after the application of the potassium 

 permanganate the nucleus gradually grew brighter, more opaque, 

 and somewhat mottled, and became the most striking feature of 

 the cell. Its outline became sharp and clear and it appeared to 

 have an enclosing membrane. Accompanying these changes in 

 the nucleus there was often a slight alteration in form, in that it 

 tended to become more spherical as though taking up fluid. 

 Finally, vacuoles of clear colorless fluid were exuded from the 

 periphery of the nucleus. As these vacuoles increased in size 

 they pushed away the surrounding cytoplasm on the one side 

 and indented the nucleus on the other, so that the latter, as it 

 condensed, became more or less crenated or pycnotic. These 

 pycnotic nuclei stood out very prominently in the cell and in 

 fixed specimens stained deeply with iron haematoxylin, like the 

 chromatin. Nuclei, which were completely surrounded by 

 vacuoles did not, as a rule, appear as irregular as those with 

 only two or three vacuoles. Not all of the larger nuclei, how- 

 ever, showed this vacuolar formation and shrinkage, since a few 

 in every culture retained more or less their usual size and shape 

 (fig. 16). The position of origin, the size and the number of 

 the vacuoles varied from one or two or several (figs. 8, 9, 10, 2) 

 to many (figs. 13, 14, 15). It is possible that the variations in 

 the number and size of the vacuoles or the total amount of fluid 

 exuded and in the correlated size of the shrunken nucleus, 

 depended, in part at least, on the condition of the nuclei (with 

 reference to age) as regards the relative amount of chromatin 

 substance and nuclear sap. Young nuclei of daughter cells have 

 very little nuclear sap and a comparatively large amount of 

 chromatin. The old resting nuclei have a greatly increased 

 actual amount of nuclear sap and also an increase in the amount 

 of chromatin, but the proportion of chromatin to nuclear sap is 

 much less than in the young cells. In most fixed cultures nuclei 

 vary in size and depth of stain. The smallest and most deeply 

 stained nuclei are the youngest, namely, those of the daughter 



