BY LR. KLEIN. 43 



selves in profile ; where tins is not the case, the surface view 

 alone is obtained. 



The Endothelium of the Serous Membranes. The 

 endotlicliuin of the serous membranes, as well as that of the 

 membranes related to them (for example, those which cover 

 the posterior surface of the cornea and the iris of mammals, 

 and the septa and walls of the lymph sacks of amphibia), is 

 well known to consist of flat cells, the substance of wlych 

 appears homogeneous when fresh, but becomes finely granular 

 by the action of certain reagents. The aucleus is .generally 

 single, and occasions a projection of the free surface. It is 

 usually oval and clear, and sometimes contains a nuclcokis in 

 its interior. Some-jiells , contain two nuclei. By reason of 

 the homogeneity of its protoplasm, the cndothelium of the 

 serous membranes is, with difficulty, brought into view in the 

 fresh state. In folds, indeed, of a serous membrane which 

 has been spread out upon a slide in a solution of common salt 

 or in other indifferent reagents, the individual cells may be 

 recognized in profile. Again, on the omentum, and on certain 

 parts of the pleura of many animals, there occur bodies 

 (which were first described by Sanderson as structures re- 

 sembling lymph follicles, and which we shall describe at 

 length in another place), the endothelium covering which may 

 be seen in the fresh state to naiat. r>f grrmi llg1 ' ^ lla w]>i ^ 

 are polyhedral, but rounded on their free surfaces, each in- 

 closing a rounded nucleus. On the fenestratecl portion of the 

 omentum, also, spots are met with where granular cells of the 

 same form occur in groups, the elements of which appear to 

 sprout out as it were frpm a common stem. Cells of the same 

 kind are also found on the abdominal surface of the centrum 

 tendineum of the diaphragm, over the structures to be after- 

 wards described as lymph channels. Further, as we have 

 already had occasion cursorily to remark, there occurs, in the 

 mesentery and parietal peritoneum, and in the female of Bufo 

 and Rana, on the septum separating the cisterna ly mphatica 

 magna from the peritoneal cavity, between the non-ciliated, 

 homogeneous, large and flat endothelial cells, other9-w4ek-are 

 ciliated,- -granular, small, and polyhedral, occuring either 

 singly or in groups. To bring these into view we have simply, 

 as we have said, to remove a portion of the membrane in 

 question from the recently killed animal, to spread it out 

 .carefully upon a slide with a couple of needles, avoiding all 

 unnecessary dragging, and to cover it quickly before it be- 

 comes dry, with a cover-glass, on which a small drop of 

 half per cent, solution of common salt, serum, or aqueous 

 humor has been placed. 



The Silver Method. The best method, however, and the 

 one most frequently employed for exhibiting endothelkm, is 



