074 VERHOEFF AND BELL. 



after the most intense exposures. Some nuclei show distortion, due 

 possibly to the uneven compression of the swollen cells, and some stain 

 less deeply than is normal, but following exposures through a crown 

 screen fragmentation is seldom observed. Marked nuclear changes are 

 seen after long exposure to the magnetite arc through the double lens 

 system without a screen, but even then only relatively few nuclei are 

 affected. Ten hours after such an exposure nuclei here and there 

 show the following changes : The nucleus becomes transparent and its 

 chromatin converted into coarse deeply staining granules attached 

 to the nuclear membrane. The transition of a normal nucleus into 

 this state is evidently very alirupt. The nucleus then becomes 

 polymorphous in shape and undergoes fragmentation. Usually the 

 fragments are each bordered by nuclear membrane and contain one 

 or more coarse chromatin granules. 



Mitotic figures are first seen after about 48 hours among the 

 unexposed cells just outside the wall where they occur in large num- 

 bers. After 5 days they are greatly diminished in number here. 

 After 3 days a few may also be found in the wall itself. Within 

 the exposed area mitotic figures are not seen until about the fifth day 

 when they occur in considerable numbers. At this time the cells are 

 still swollen. The basophilic granules are little if any changed except 

 possibly they are more often irregular in shape, but the eosinophilic 

 granules have largely become confluent and are apparently under- 

 going solution. The mitotic figures are never seen in cells containing 

 granules. Many of the nuclei are abnormally large and show early 

 stages of direct division and budding. 



At the end of ten or twelve days the cells have almost entirely lost 

 their swollen appearance and the basophilic and eosinophilic granules 

 have almost entirely disappeared. The most striking feature now 

 consists in the inequalities in sizes and shapes of the nuclei. Most of 

 the nuclei are abnormally large; occasionally one has three times the 

 diameter of a normal nucleus. Some are abnormally small. Many 

 of the nuclei evidently are undergoing direct division, as all the stages 

 in this process can be seen, from a slight constriction of the nucleus to 

 two nuclei connected by a delicate strand. In addition to this, a 

 process of budding can similarly be traced, the nuclei becoming poly- 

 morphous in shape and constricting off buds varying in size from that 

 of a normal nucleolus to half that of a normal nucleus. Some cells 

 contain as many as twelve of these free buds. The buds have the 

 reticulated structure, staining reaction and general appearance of the 

 nucleus proper, and each most often contains a nucleolus. Cells 



