216 Experimentation upon Animals 



having a piston to come into contact with the fluid to 

 be injected. This is, however, really disadvantageous, 

 inasmuch as the cushion of compressed air that drives out 

 the contents is elastic, and unless carefully watched will 

 follow the injection into the body of the animal. In making 

 subcutaneous injections there is no disadvantage or danger 

 from the entrance of air, but in intravenous injections it is 

 extremely dangerous. 



Syringes with metal or glass pistons are excellent, though 

 not very durable. All syringes should be disinfected with 5 

 per cent, carbolic acid solutions before and after using, the 

 carbolic acid being allowed to act for some time and then 

 washed out with sterile water. Syringes should not often be 



=1 



Fig. 59. 1, Roux's bacteriologic syringe; 2, Koch's syringe; 3, 

 Meyer's bacteriologic syringe. 



boiled, as it ruins the packings, whether of asbestos, leather, 

 or rubber. 



The intravenous injections differ only in that the needle 

 of the syringe is introduced into a vein. This is easy to 

 achieve in a large animal, like a horse, but is very difficult 

 in a small animal, and well-nigh impossible in anything 

 smaller than a rabbit. Such injections, when given to rab- 

 bits, are usually made into the ear-veins, which are most 

 conspicuous and accessible (Fig. 60). A peculiar and im- 

 portant fact to remember is that the less conspicuous poste- 

 rior vein of the ear is much better adapted to the purpose 

 than the anterior. The introduction of the needle should be 

 made from the hairy external surface of the ear when the 

 vein is immediately beneath the skin. 



If the ear be manipulated for a moment or two before the 



