USE OF ANIMALS 167 



thetics can be used in many cases. An anesthetic should be- 

 given when the suffering from the operation is severe, or 

 greater than the disagreeable effects of the ether, or when the- 

 operation is difficult to perform. 



Restraining animals for inoculation. In making inocu- 

 lations guinea pigs are held, as a rule, by an assistant who* 

 holds in one hand the forelegs and in the other the hind legs. 

 The animal should rest flatly upon the table in order to avoid 

 injury to the back from wrenching. Rabbits can be held in 

 the same manner or it may be better to avoid injury by using 

 some holder. 



Mice, which are usually inoculated subcutaneously in the 

 body at the root of the tail, may be placed in a mouse holder. 

 A convenient substitute is to grasp the tail in a pair of lab- 

 oratory tongs, and then, while allowing it to hang head down- 

 ward in a jar, a glass plate is pushed across the top until only 

 space for its tail and rump is left. In this position it is easy 

 to make the subcutaneous injection with the hypodermic- 

 needle. 



All these methods must be carried out with the greatest 

 care as to cleanliness. The hair should be clipped and the 

 skin at the point of injection disinfected. The operator must 

 be careful not to infect himself or his surroundings. After 

 the inoculations are made the animals should be given the 

 best of care, unless, for special purposes, we want to study 

 them under unusual conditions. For food, rabbits and guinea 

 pigs require only carrots and hay. Other food may be given 

 but green or fresh vegetables must accompany grain or dry 

 hay. The autopsy should be made at the earliest moment 

 possible after death before post mortem changes occur. If 

 delay is unavoidable, the animals should be placed immedi- 

 ately after death in a cold place. In making cultures from 

 the dead bodies the greatest care should be taken to avoid 

 contamination. The skin should be moistened with a disin- 

 fectant such as a 5 per cent solution of carbolic acid. All in- 

 struments are sterilized by boiling in water or a 3 per cent 

 soda solution for five minutes. Change of knives, scissors; 



