BY DR. BURDON-SANDERSON. 241 



to have recourse to more complicated appliances and appa- 

 ratus. 



The mesenteries of small rodents have been repeatedly used 

 for the demonstration of the mammalian capillary circulation. 

 These, however, are not to be compared, as subjects of obser- 

 vation, with the omentum, and particularly with that of the 

 guineapig. This structure forms a delicate membranous ex- 

 pansion of from twelve to fifteen cubic centimetres in extent, 

 which is attached by its upper margin to the greater curvature 

 of the stomach. It differs from the organ of the same name in 

 man in consisting, for the most part, of only two layers of 

 peritonaeum, in being much more delicate in its structure, and 

 containing very little fat. Hence, from the simplicity of the 

 anatomical relations, and particularly from its being attached 

 by one side only to the stomach, from its perfect transparency, 

 from its abundant vascularity, and, lastly, from its containing 

 not only vessels but living cells, it is obvious that this mem- 

 brane offers a good field for research. 



The observations hitherto made on the mammalian mesen- 

 tery have been without practical result, the reason being that 

 so vulnerable a tissue as that of the peritonaeum cannot be 

 exposed, even for a few minutes, without injury; so that, 

 although the greatest care is taken in demonstration, only a 

 momentary glimpse can be obtained. To obviate this difficulty, 

 the arrangements for placing the membrane under the micro- 

 scope must be of such a nature, that the structure is bathed 

 during the whole period of observation in a liquid at the tem- 

 perature of the bod}'. It need scarcely be said that water, 

 from its destructive influence on living tissues, would not 

 answer the purpose. Serum would probably be best, if it were 

 always at hand ; but, practically, solution of common salt of 

 the strength ordinarily used (f per cent.) answers the purpose 

 perfectly. The temperature is maintained by keeping the 

 glass trough, in wlrich the membrane is spread out, over the 

 warm stage, the construction of which has been already de- 

 scribed. 



The mode of procedure is as follows: The guineapig is first 

 placed under the influence of chloral by injecting that sub- 

 stance in solution under the skin, three grains being required 

 for an animal about lib. in weight. It is then laid on a sup- 

 port, the upper surface of which is on the same horizontal 

 plane as that of the microscope-stage. An incision not more 

 than an inch in length is next made, extending outwards from 

 the edge of the left rectus muscle a little below the end of the 

 ensifonn cartilage. The muscles having been divided, and the 

 peritonaeum cautiously opened for about half an inch, or even 

 less, the free edge of the omentum is carefully drawn out. It 

 must then be floated in the warm bath prepared for it, and is 

 16 



