CIRCULATION IN THE MESENTERY, 157 



All that remains to be done is to place the extruded 

 mesentery over the aperture, and to keep it in posi- 

 tion by two or three fine needle points passed through 

 the surrounding intestine into the cork. In this 

 case again, the greatest care must be taken in no 

 way to drag upon the exposed membrane, or to 

 allow it to be pressed upon. Moreover, the surface 

 must from time to time be moistened with a little 

 salt solution, to prevent its becoming dry. But in 

 spite of every precaution the mere exposure of the 

 serous surface to the air is sufficient to produce 

 before long the changes in the circulation which 

 are characteristic of the commencement of inflam- 

 mation. 



Preparation 8. Capillary circulation in 



Mammals. It is less easy to study the circulation in 

 the serous membrane of mammals, for the exposure re- 

 quired for the purpose is apt to be far more prejudicial to 

 the maintenance of the normal condition of the tissues 

 than is the case with the cold-blooded vertebrates. It is 

 necessary, moreover, to maintain the exposed part at the 

 body temperature, and to immerse it in fluid, since it 

 would otherwise become at that temperature rapidly 

 desiccated. The membrane generally chosen is not the 

 mesentery but the omentum, which in many animals, e.g. 

 the guinea-pig, is very extensive, and at the same time 

 thin, and provided in parts with a sufficient number of 

 bloodvessels. The animal, whieh should be rather a 

 small one, is anaesthetized with chloral hydrate, a few 

 minims of a 50 per cent, solution being injected under 

 the skin. The warm stage (Fig. 9) is in the meanwhile 

 got read}', and a glass tray (which can be extemporized 

 out of a small plate of glass, some pieces of glass rod and 

 sealing-wax) is placed on it and filled with salt solution, 

 which is maintained at about 38 C. Then the animal 

 is supported on a block at a convenient level, and the 

 abdomen having been carefully opened, a little of the 

 omentum is drawn out and allowed to float flat in the 

 warm salt solution, where it can be examined either with 

 a low power or with an immersion objective dipping into 

 the solution. If the latter be employed a piece of thin 

 14 



