224 Experimentation upon Animals 



contents is elastic, and unless carefully watched will follow the injec- 

 tion into the body of the animal. In making subcutaneous injec- 

 tions 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 like those shown are to be 

 preferred. All syringes should be disinfected by boiling thoroughly, 

 before and after using. Syringes with packings to tighten the pistons 

 cannot be boiled with impunity, as it soon ruins them, and new pack- 

 ings may be difficult to obtain or fit. Syringes of such design should 

 be avoided. 



The intravenous injection is easy to achieve in a large animal, like 

 a horse, but is very difficult in animals smaller than a rabbit. Such 

 injections, when given to rabbits, are usually made into the ear- 

 veins, which are most conspicuous and accessible. A peculiar and 

 important fact to remember is that the less conspicuous posterior 

 vein of the ear is much better adapted to the purpose than the an- 

 terior. The introduction of the needle should be made from the 

 hairy external surface of the ear where the vein is immediately beneath 

 the skin. 



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

 vasomotor dilatation occurs and the blood-vessels become larger and 

 more conspicuous. The vein should be compressed at the root of the 

 ear until the needle is introduced, and the injection made as near the 

 root as possible. The fluid should be injected slowly. 



By using very fine needles, similar injections may be made into the 

 ear veins of guinea-pigs. By dipping the tails of rats and even mice 

 into warm water so as to cause dilatation of the caudal veins, it may 

 be possible to effect intravenous injections of such animals. Kolmer 

 suggests that the tails be vigorously rubbed with xylol or alcohol, 

 and the epidermal cells softened and scraped off so as to expose the 

 veins better. As the first attempt to get the needle into the caudal 

 vein may fail, and new attempts be required, it is well to begin at a 

 point not too near the body. 



Bacteria can be introduced into the lymphatics only by injecting 

 liquid cultures into some organ with comparatively few blood-vessels 

 and large numbers of lymphatics. The testicle is best adapted to 

 this purpose, the needle being introduced deeply into the organ. 



Sometimes subcutaneous inoculations are made by introducing the 

 platinum wire through a small opening made in the skin by a snip of 

 the scissors. By this means solid cultures from agar-agar, etc., can be 

 introduced. 



Intra-abdominal and intrapleural injections are sometimes made, 

 and in cases where it becomes necessary to determine the presence 

 or absence of the bacilli of tuberculosis or glanders in fragments of 

 tissue it may be necessary to introduce small pieces of the suspected 

 tissue under the skin. To do this the hair is closely cut over the 

 point of election, which is generally on the abdomen near the groin, 



