24:6 The Miokoscopb. 



For the study of the cells found in this tissue, the mesentery, 

 prepared as just described, will answer. The intermuscular fasciae, 

 when spread out and stained, show numbers of stellate cells. Exam- 

 ine also the tail of a tadpole or the web of a frog's foot. The stel- 

 late cells will be found loaded with pigment, with the exception of 

 the nucleus, which is generally clear. 



Endothelium. — These cells which cover with a single layer the 

 serous membranes and line the various closed cavities, as the interior 

 of blood-vessels, etc., have often been described in connection with 

 epithelium. They are not, however, epithelial in character, but are 

 fixed connective-tissue cells. They can be most easily demonstrated 

 in the frog's mesentery as follows: Wash a small piece of the 

 membrane carefully in distilled water, then immerse it in the silver- 

 nitrate solution. Leave it there for two or three minutes, then 

 remove and wash again. Now place it in a vessel of distilled water, 

 cover with a glass plate and expose to the light — not direct sun-light, 

 however — until it assumes a light-brown color. This usually takes 

 a number of hours, during which time the water may be changed a 

 few times. The color appearing, the membrane will have been 

 sufficiently stained to show the outlines of the cells. This result is 

 produced by the combination of the silver salt with the intercellular 

 substance to form an albuminate, which, white at fii'st, darkens on 

 exposure. The specimen may now be stained with hamatoxylin, 

 cleaned, dehydrated and mounted in balsam. In carefully focussing, 

 the delicate network will come into view, blackened by the silver, 

 the nuclei, large and delicate, taking the logwood stain. 



EDITORIAL.. 



REAGENTS IN MICROSCOPY. 



TT is unfortunate that circumstances (excepting, of course, in 

 -*■ micro-chemistry), compel the use of reagents in microscopy, and 

 too much care cannot be taken in the study of tissues to eliminate, 

 as far as possible, the effects these reagents may have upon them. 

 The hardening, the embedding, the staining, etc., of tissues, all tend 

 to alter, somewhat, their apparent structure. In fact, the only ideal 

 way to study organic objects is to employ fresh or living tissues, and 

 to examine them under their natural conditions. Such a way, how- 

 ever, is impossible, and we must, through necessity, make use of 

 chemicals, the effects of which on the tissues we oftentimes know 

 little about. But we should not make a virtue of this necessity. We 



