94 EXPERIMENTS UPON ANIMALS. 



dry heat. The objection to most syringes used for this pur- 

 pose is that the packing is made of rubber or leather, and 

 cannot be sterilized by heat of any kind. The syringes and 

 all other apparatus used in the performance of these animal 

 experiments should be sterilized thoroughly both before and 

 after using. 



Inoculations are made also with the platinum needle, which 

 is passed in through a small opening made in the skin. 



No matter where nor how the inoculation is to be made, 

 the first steps are to remove all hair from the site of inocu- 

 lation with scissors and a razor; and then to disinfect the 

 skin in order to avoid any possible contamination or in- 

 fection with pus cocci. Some bacteriologists advise snipping 

 off a small piece of skin with curved scissors, of a size suf- 

 ficient not to draw blood, but to remove the surface epithelium, 

 thus leaving a denuded spot through which the needle can be 

 introduced. This absolutely precludes the possibility of con- 

 taminating the injection. 



Fluids in large quantities are injected into the circulation 

 or into the peritoneal cavity by forcing them through a 

 slender canula with a syringe or rubber bulb. 



When injections are made into the peritoneal cavity, care 

 must be taken not to injure any of the abdominal organs. 

 The intestines usually slip out of the way of the advancing 

 needle or canula, and are not so apt to be injured as the liver 

 or stomach. The injection is made in the same manner as 

 is any hypodermic injection and under the same antiseptic 

 precautions. 



Intravenous inoculation is done usually on rabbits because 

 the ear vein of the rabbit is conspicuous and within easy 

 reach. Small animals are unsuited for this form of inocula- 

 tion. After thoroughly cleansing the ear the veins are dis- 

 tended momentarily by compressing them at the base of the 

 ear. The needle is introduced at the root of the ear, point- 

 ing in the direction of the current of blood, and the injection 

 made slowly. The puncture is sealed with collodion. 



For subcutaneous injections, mice are used. The inocula- 

 tion is made at the root of the tail, where a little pocket is 

 made for the reception of the material. 



