EXPERIMENTS UPON ANIMALS. 97 



Large quantities of fluid may be injected into the cavity of the 

 abdomen or into the circulation by slowly forcing the fluid through 

 a slender canula, properly introduced, which is coupled with a large 

 syringe by means of rubber tubing, or with a glass receptacle from 

 which the fluid is forced by the pressure of air pumped in with a 

 rubber hand ball. 



Mice are usually injected subcutaneously near the tail. The 

 little animal is first seized by a long pair of forceps, or "mouse 

 tongs," and the hair is clipped away on the back just above the tail. 

 If solid material is to be introduced a little pocket is made with scis- 

 sors or with a lancet, into which the infectious material is carried by 

 means of a platinum needle or slender forceps. Liquids may be in- 

 jected by the little glass syringe heretofore described, the point of 

 which is easily forced through the skin. 



Pasteur's method of inoculating rabbits with the virus of hydro- 

 phobia consists in trephining the skull and injecting the material 

 beneath the dura mater. An incision through the skin is first made 

 to one side of the median line a short distance back of the eyes. 

 The edges of the wound are separated, and a small trephine (five or 

 six millimetres in diameter) is used to remove a button of bone. The 

 emulsion of spinal cord from a hydrophobic animal is then carefully 

 injected beneath the dura mater two or three drops will be sufficient. 

 The wound is washed out with a two-per-cent solution of carbolic 

 acid and closed with a couple of sutures. 



Injections into the intestine are made by carefully opening the 

 abdomen with antiseptic precautions, gently seizing a loop of the in- 

 testine, and passing the point of the syringe through its walls ; the 

 loop is then returned and the incision in the walls of the abdomen 

 carefully closed with sutures and dressed antiseptically. 



Inoculations into the anterior chamber of the eye of rabbits and 

 other animals have frequently been practised, and offer certain ad- 

 vantages in the study of the local effects of pathogenic microorgan- 

 isms. The animal should be fastened to an operating board, belly 

 down, and its head held by an assistant, who at the same time holds 

 the eyelids apart. The conjunctiva is seized with forceps to steady 

 the eye, and an incision about two millimetres long is made through 

 the cornea with a cataract knife. Through this opening a small 

 quantity of a liquid culture may be injected, or a bit of solid material 

 introduced with slender curved forceps. 



Ordinary injections give but little pain and do not call for the use 

 of an anaesthetic. When anaesthesia is required ether will usually 

 be preferable to chloroform. Rabbits, especially, are very apt to die 

 from chloroform, no matter how carefully it may be administered. 

 Dogs, rats, and mice stand ether very well. The smaller animals 

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