INJECTING THE LOWER ANIMALS. 251 



After the second injection has been made, pieces of kid- 

 ney which have become of a bluish colour are cut off with 

 a razor, and steeped in a one per cent, of osmic acid, in 

 which the pieces must be left to harden from twelve to 

 twenty-four hours. They should be small enough to 

 allow the osmic acid to penetrate freely. After they 

 are removed from the acid, they must be thrown into 

 distilled water for half an hour, and finally kept for 

 examination in alcohol. This method imparts a bluish 

 tint, with a tinge of violet, to the protoplasm and 

 nucleus, whilst the cells of the straight tubules receive 

 no coloration. 



Injecting the Lower Animals. The vessels of fishes 

 are exceedingly tender, and require great caution in 

 filling them. It is often difficult or quite impossible 

 to tie the pipe in the vessel of a fish, and it will 

 generally be found a much easier process to cut off 

 the tail of the fish, and put the pipe into the divided 

 vessel which lies immediately beneath the spinal 

 column. In this simple manner beautiful injections of 

 fish may be made. 



Mollusca. (Slug, snail, oyster, &c.) The tenuity of 

 the vessels of the mollusc often renders it impossible 

 to tie the pipe in the usual manner. The capillaries 

 are, however, usually very large, so that the injection 

 runs very readily. In different parts of the bodies of 

 these animals are numerous lacunas or spaces, which 

 communicate directly with the vessels. Now, if an 

 opening be made through the integument of the 

 muscular foot of the animal, a pipe may be inserted, 

 and thus the vessels may be injected from these lacunae 

 with comparative facility. 



Insects. Injections of insects nid,y be made by 

 forcing the injection into the general abdominal 

 cavity, when it passes into the dorsal vessel and is after- 

 wards distributed to the system. The superfluous 

 injection is then washed away, and such parts of the 

 body as may be required, removed for examination. 



Injection of Invertebrate Animals. Gr. Joseph uses 

 filtered white of egg, diluted with 1 to 5 per cent, of 

 carmine solution, for cold injections. This coagulates 



