METHODS OP INFECTION. 265 



or guinea- pig should be held on its back by an assistant. The head and 

 front legs should be held in the pa,lm of the left hand, while the hind 

 legs are held down firmly with the right. A very convenient way of 

 holding a rabbit is for the assistant to take it by the ears and hind 

 legs and stretch it over his hip or knee. 



Guinea-pigs may be inoculated without the aid of 

 an assistant by placing these within an ordinary large 

 graduate cylinder. A cylindrical holder of 

 copper, as described byVoges, is preferable to 

 the use of a glass one. Fig. 44 illustrates the 

 manner of using these holders. It is well to 

 have 2 or 3 of these cylinders of different diam- 

 eters, so as to fit guinea-pigs of various size. 

 The length should be about 18 to 20 cm. The 

 diameters may be 6 and 8 cm., respectively. F1G.43. sterile 

 The longitudinal slit should be about 1 cm., 

 wide and 10 cm. long. Equally useful holders can be 

 made by boring holes, of the size given, in a block of 

 wood. 



The mouse or rat is usually picked up by the tail with a pair of 

 rat forceps (Fig. 46 6) and set on the table. A folded piece of cloth is 

 dropped on its head, which is then seized between the thumb and fin- 

 ger. The tail and hind legs are held by the other hand. When hold- 

 ing the animal thus, the pressure should be applied to the head and 

 not to the neck or chest. A better procedure than the above, which, 

 moreover, dispenses with the need of an assistant, is to grasp the ani- 

 mal by the nape of the neck in a Collin pressure forceps. The forceps 

 are now suspended from a hook or from a retort stand, and the tail 

 and hind legs grasped in the fingers of the left hand. The animal is 

 thus placed on a slight stretch and the inoculation is made with the 

 right hand. 



3. — Intravenous injection. — The direct introduction into 

 the circulation of a bacterial suspension or toxin is fre- 

 quently practised. This method is especially valuable in 

 the immunization of animals. Inasmuch as the liquid is in- 

 troduced directly into the blood current, and is thus rapidly 

 distributed throughout the body, it follows that the results 



