DETERMINING BIOLOGICAL ACTIVITIES OF BACTERIA 203 



intravenous, or subdural, etc. It must be borne in mind always 

 that the mode of inoculation may influence the course of an infection 

 no less than does the virulence of the microorganism or the size 

 of the dose. 



Inoculations are made with some form of hypodermic needle 

 fitted to a syringe. The most convenient syringes are the all-glass 

 Luer or the Debove syringes, which, however, are expensive. Any 

 form of sterilizable syringe may be used. In making inoculations 

 the hair of the animal should be clipped and the skin disinfected 

 with carbolic acid or alcohol. 



Subcutaneous inoculations are most conveniently made in the 

 abdominal wall, where the skin is thin. After clipping and steriliz- 

 ing, the skin is raised between the fingers of the left hand and the 

 needle plunged in obliquely so as to avoid penetrating the abdominal 

 wall and entering the peritoneum. 



In making intraperitoneal inoculations, great care must be exer- 

 cised not to puncture the gut. This can be avoided by passing the 

 needle first through the skin in an oblique direction, then turning 

 it into a position more vertical to the abdomen and perforating the 

 muscles and peritoneum by a very short and carefully executed stab. 



Intravenous inoculations in rabbits are made into the veins run- 

 ning along the outer margins of the ears. The hair over the ear 

 is clipped and the animal held for a short time head downward 

 so that the vessels of the head may fill with blood. An assistant 

 holds the animal firmly in a horizontal position, the operator grasps 

 the tip of the ears with the left hand, and carefully passes his needle 

 into the vein in the direction as nearly as possible parallel to its 

 course. 



Mice are usually inoculated under the skin near the base of 

 the tail. They may be placed in a jar over which a cover of stiff 

 wire-gauze is held. They are then grasped by the tail, by which 

 they are drawn up between the side of the jar and the edge of the 

 wire cover, so that the lower end of the back shall be easily acces- 

 sible. The skin is then wiped with a piece of cotton dipped in 

 carbolic solution and the needle is inserted. Great care must be 

 exercised to avoid passing the needle too close to the vertebral 

 column. Mice are extremely delicate, and any injury to the spine 

 usually causes immediate death. 



With proper care mice or rats may be easily injected intra- 

 venously if a sufficiently fine needle is used. There are four super- 



