365 



other from the rapid evaporation of the solution, and the con- 

 sequent alteration of its density, and eventual desiccation of 

 the membrane. The first difficulty is obviated by warming 

 the objective ; the second by providing for the renewal of the 

 water contained in the bath by the constant influx of fresh 

 water at a rate corresponding to that at which it wastes. 



The operative procedure is extremely simple. The guinea- 

 pig having been thoroughly chloralised, is laid on a support 

 or block, the upper surface of which is in the same horizontal 

 plane with that of the microscope stage. An incision is made, 

 which extends for two inches at most, from the outer edge of 

 the left rectus muscle, a little below (behind) the end of the 

 ensiform cartilage horizontally cut out so as to divide one or two 

 costal cartilages. The muscles must next be divided and the 

 peritoneum carefully opened. The stomach can then be drawn 

 out of the abdominal cavity without difficulty, especially if 

 the additional precaution be emiployed of first removing some 

 of its contents. In doing this, very little manipulation is 

 necessary, and special care must be taken to avoid touching 

 the delicate structure attached to its border which is to be 

 subjected to observation. The moment that the organ is 

 fairly out of the abdomen, the membrane must be floated 

 into the warm bath prepared for it, and is then ready for 

 examination. It is, however, found very advantageous to 

 cover those parts of it which do not lie directly under the 

 microscope with sheets of blotting-paper. This arrangement 

 has two advantages ; the risk of evaporation is diminished, 

 and the undulatory movements of the water are prevented, 

 so that the object is rendered much steadier than it would 

 otherwise be. The enlargements we have hitherto employed 

 are inconsiderable, the most useful object being the 

 quarter of Ross. We have no doubt, however, that we shall 

 eventually be able to apply both air and immersion objec- 

 tives of higher magnifying power. 



The objects which present themselves to the observer in 

 the omentum of the guinea-pig are manifold. We content our- 

 selves with barely enumerating them. Veins and arteries 

 may be studied of various diameters, some of them 

 surrounded by sheaths containing fat-cells, some by similar 

 sheaths containing the cells of which mention has already 

 been made, others so free that their structure can be perfectly 

 studied. Labyrinthine capillaries of surpassing beauty can be 

 studied both in the sheaths of the vessels and in the little 

 nodules of tissue in their neighbourhood, and finally the 

 epithelial elements with their characteristic spheroidal nuclei 



VOL. X. NEW SER. B B 



