672 VERHOEFF AND BELL. 



the simplicity of its structure and abundance of its cells, and because, 

 by means of the flat preparations described (page 660) the whole of 

 the exposed area may be examined at once. Moreover, the effects 

 produced in it are not complicated by the presence of leucocytes, 

 since these cannot penetrate it. Following are the histological 

 changes produced in the epithelium by abiotic radiations: 



If the capsule is fixed immediately after exposure, even if the latter 

 has been prolonged, the cells appear absolutely normal. After 

 24 hours, changes are well marked, and reach their maximvmi in from 

 48 to 72 hours. After severe exposures, the cells may be so greatly 

 affected that many of them no longer adhere to the capsule unless 

 the latter is fixed within 24 hours. It is noteworthy that the cells 

 in the exposed area are not all affected alike and one cell, or group 

 of cells, may be markedly affected while the neighboring cells are 

 only slightly affected. The chief changes noted consist in (a) 

 swelling of the cells, (b) the appearance of granules in the cyto- 

 plasm, and (c) the formation of a peripheral wall of cells. 



(a) After short exposures swelling of the cells may be almost 

 the only change noted. It is plainly evident after an interval of 

 20 hours, but does not reach its maximum until after 48 hours. 

 It is associated with increased transparency of the cytoplasm. All 

 the cells do not swell to an equal extent, and as a result of the 

 inequalities in compression the cells become misshapen in an irregular 

 manner. 



(b) The granules (PI. 2, Figs. 5 and 6) in the cytoplasm first appear 

 before the cells become much swollen. They are present within 10 

 hours but are more abundant after 48 hours. While evidently in the 

 case of any individual cell a greater exposure is necessary to produce 

 them than is required to produce swelling alone, a few cells contain- 

 ing them may always be found if the epithelium is affected at all. 

 The longer the exposure the greater the number of cells containing 

 them, and also the greater the number of granules in each cell, so 

 that after prolonged exposures almost every cell may contain them. 

 The granules are of two kinds. The more abundant are more or less 

 strongly eosinophilic, usually round in shape and varied in size, the 

 largest exceeding half the size of the nucleus. One cell may contain 

 from one to over twenty granules. Each usually appears to be situ- 

 ated in a vacuole which it does not quite fill, but this may be due to 

 shrinkage as a result of fixation. Close examination shows that they 

 have a reticulated and subgranular structure. The other granules 

 are intensely basophilic, and smaller than the eosinophilic granules. 



