METHODS OF ANIMAL EXPERIMENTATION 137 



manipulations are to be carried out. For operations requiring 

 some time the animal is fastened to a board with stout cords, or 

 is held by means of a specially constructed animal holder. 



Inoculation.' — Infectious material may be introduced into 

 the animal body in various ways. The most common methods 

 are injection under the skin and injection into the peritoneal 

 cavity. The. hair should be removed from the site selected. 

 A sterilized hypodermic syringe is used, and it is again sterilized 

 by boiling after use. Subcutaneous injection is usually made 

 in the thoracic region as one easily avoids penetrating the chest 

 cavity. For intraperitoneal injection the needle is quickly thrust 

 through the abdominal wall. 



Inoculation into the cranial cavity is practised especially in 

 studying rabies. The animal, rabbit or guinea-pig, is anesthe- 

 tized and the scalp is shaved. An incision through the scalp 

 about 8 to 10 mm. long is made at the left of the median line 

 and parallel with it, a little in front of a line connecting the 

 external auditory openings. The scalp is then forcibly drawn 

 over to the right and a hole drilled through the skull at the right of 

 the median line. A sharp-pointed scalpel may serve the purpose 

 of a drill. The needle is then inserted into the cerebral substance 

 nearly to the floor of the cranial cavity and the material (o.i 

 to 0.5 c.c.) injected. Any blood or fluid is taken up with sterile 

 absorbent cotton. The skin is replaced in its original position 

 and may be dressed with cotton and collodion, although dressing 

 may be omitted altogether. 



Inoculation into the circulating Hood is a method of special 

 importance. "In rabbits intravenous injection is easily done. 

 The hair is removed from the ear over the marginal vein, and 

 the vein is dilated by application of a hot towel, after which the 

 skin is wiped dry. An assistant constricts the base of the ear 

 to congest the vein and the needle is easily inserted into it. Other 

 veins on the ear may be used, but they are not so easily penetrated 

 by the needle. In rats, guinea-pigs or monkeys, intravenous 

 injection is not so simple and it is easier to inoculate these animals 



