136 PEACTICAL HISTOLOGY [XVII 



possible. Cut across the inferior vena cava, and sponge up the 

 blood. 



Pick up the cut edge of the aortic bulb with fine-pointed 

 forceps, and put into the bulb and up the left aorta a fine 

 nozzled cannula, provided with an inch or so of india-rubber 

 tubing. Tie in the cannula, fill it with '75 p.c. sodium sulphate 

 and pinch the tubing, in order to drive blood out of the nozzle 

 of the cannula, where it would rapidly clot. 



Fill the cannula again ; take a 5 to 10 c.c. injection syringe, 

 the nozzle of which fits the india-rubber tubing, fill it with 

 75 p.c. sodium sulphate, and push the nozzle into the tubing, 

 pinching the tubing as the nozzle is inserted, so as to avoid 

 air-bubbles. 



Inject the sodium sulphate, sopping up with a sponge the 

 fluid which comes from the cut vessels; and now and then 

 stroking the abdomen upwards. When the fluid is nearly 

 colourless (injection of one syringe-full should be sufficient), 

 inject in the same way a syringe-full of 0'2 p.c. nitrate of 

 silver. 



Leave for five minutes. Inject a syringe-full of distilled 

 water. Then put the frog in distilled water. Expose the viscera 

 freely, and cut out the following tissues and expose to light 

 in distilled water. The bladder: lift it up by the ends, cut 

 through the membrane attached to it ; remove it and cut it open. 

 The intestine and mesentery: lift up the end of the rectum, 

 cut through the mesentery at its dorsal attachment and remove 

 it with the intestine, cut off the mesentery and take the largest 

 pieces ; cut open the intestine, scrape off the mucous membrane, 

 and pin out the muscular coat with quills. (The lungs, pinned 

 out, and the kidneys should also be taken ; the latter will show 

 the epithelioid cells of the capsules.) When the tissues show 

 signs of reduction, dehydrate pieces keeping them stretched 

 out and mount in balsam. 



Note the outlines of the flat elongated epithelioid cells of the 

 arteries, of the capillaries and of the veins ; the outlines in the 

 capillaries are more irregular than in the arteries or veins; in 

 the veins the cells are rather broader than in the arteries. In 

 the larger vessels the cement substance between the cells of the 



