EXPERIMENTS UPON ANIMALS. 77 



some large stall or inclosure. They can be fed upon all sorts of 

 vegetables and grasses, and require but little attention. 



Methods of Inoculation. /. Inhalation. Imitating the natural 

 infection, either by loading an atmosphere with the germs in 

 question or by administering them with a spray. 



//. Through Skin or Mucous Membrane. 



III. With the Food. 



Method of Cutaneous Inoculation. The ear of mice is best 

 suited for this procedure. A small abrasion made with the 

 point of a lancet or needle, which has been dipped in the virus. 

 The animal is then separated from the rest and placed in a 

 glass jar, which is partly filled with sawdust and covered with 

 a piece of wire-gauze. 



Subcutaneous. The root of the tail of mice is used for this 

 purpose. The hair around the root of the tail is clipped off, 

 and with a pair of scissors a very small pocket is made in the 

 subcutaneous connective tissue, not wounding the animal any 

 more than absolutely necessary, avoiding much blood. The 

 material is placed upon a platinum needle and introduced into 

 the pocket, solid bodies, with a forceps. 



To hold the mouse still while the operation is going on a 

 little cone made of metal is used. The mouse just fits in here. 

 There is a slit along the top in which the tail can be fastened, 

 and thus the animal is secure and immobile. 



Intravenous Injections. Rabbits are very easily injected 

 through the veins. Mice are too small. 



The ear of the rabbit is usually taken. It is first washed with 

 1-2000 bichloride,, which not only disinfects, but also makes the 

 vessels appear more distinct. The base of the ear is compressed 

 to swell the veins. Then a syringe, like the one used for the 

 injection of " tuberculine," a Koch syringe, which can be easily 

 sterilized, is filled with the desired amount of virus and slowly 

 injected into any one of the more prominent veins present. 

 (Fig. 43.) 



Intra-peritoneal Injection. This is used with Guinea-pigs 

 mostly. The abdominal wall is pinched up through its entire 

 thickness, and the needle of the syringe thrust directly through, 

 so that it appears on the other side, then the fold let go, the 

 needle withdrawn just far enough so as to be within the cavity. 



