PRINCIPLES OF BACTERIOLOGY 



of the rabbit. If rabbits are placed in a holder, so that the rabbit 

 remains quiet and only the head projects, it is usually easy to pass a 

 small needle directly into one of the ear veins, especially those running 

 along their edges. If the ear is first moistened with a 3 per cent, car- 

 bolic acid solution, and then supported between the finger inside and 

 the thumb outside, the vein is usually clearly seen and entered with 

 ease, if a small, sharp needle is held almost parallel with the ear surface 

 and gently pushed into it. When no holder is present, the rabbit can 

 be held by an assistant seizing the forelegs in one hand and the hind 

 in another and holding the rabbit head downward. 



4. Into the anterior chamber of the eye. 



5. Into the body cavities. The peritoneal and less often the pleural 

 cavities are used for bacterial injection. The hypodermic needle is 

 usually employed, less often a glass tube drawn out to a fine point. 

 The needle or the pointed glass tube is gently pushed through the 

 abdominal wall, moved about to ensure its freedom from the intestines, 

 and the fluid injected. 



6. By inhalation. This method is carried out by forcing the animal 

 to inhale an infected spray or dust. 



7. By the trachea. This method is carried out by making an incision 

 in the trachea and then inoculating the mucous membrane or injected 

 substances into the trachea and bronchi. 



8. Through the intestinal tract by swallowing or the passage of a 

 rubber tube. 



9. Into the brain subtance or ventricles after trephining. 



In these injections guinea-pigs are held, as a rule, by an assistant 

 grasping in one hand the forelegs and in the other the hindlegs. 



Rabbits can be held in the same manner, or, better, placed in some 

 holder or strung up by their hindlegs. 



Mice, which are usually inoculated subcutaneously in the body or 

 at the root of the tail, are best placed in a mouse holder, but can be 

 inoculated by grasping the tail in a pair of forceps, and then, while 

 allowing the mouse to hang head downward in a jar, a glass plate is 

 pushed across the top until only space for its tail is left. 



All these methods must be carried out with the greatest care as to 

 cleanliness, the hair being clipped and the skin partially, at least, dis- 

 infected. The operator must be careful not to infect himself or his 

 surroundings. After the inoculations 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. 



^ If animals die, autopsy should be made at the earliest moment pos- 

 sible, for soon after death some of the species of the bacteria in the 

 intestines are able to penetrate through the intestinal walls and infect 

 the body tissues. If delay is unavoidable, the animals should be placed 

 immediately in a cold place. In making cultures from the dead bodies 

 the greatest care should be taken to avoid contamination. The skin 

 should be disinfected, and any dust prevented by wetting with a 5 per 



