232 MANUAL OF MICROBIOLOGICAL METHODS 



Intravenous. This is a commonly used site for deposition of patho- 

 genic bacteria, toxins, and other virulent exudates. The choice of veins 

 is largely a matter of convenience and will vary with the animal. Rabbits 

 are usually injected into the marginal ear vein; mice and rats in a tail 

 vein; guinea pigs in the ear or jugular vein; horses, cows, and sheep in the 

 jugular vein; swine in the ear vein; dogs and cats in the jugular or the 

 vein crossing the inner surface of the thigh. Fowl may be injected, after 

 a little practice, in the radial vein that crosses the elbow joint of the wing. 

 Veins may be dilated by rubbing the surface of the skin with xylene- 

 soaked gauze or cotton or by warming the area with warm water. In the 

 case of rats or mice, it is simplest to immerse the tail for a few seconds in 

 a container of water adjusted to a temperature of about 45°C. If the 

 material to be inoculated is considerably acid or alkaline, it is adjusted to 

 p.H 7.3-7.4. Any coarse particles are removed by centrifugation. The 

 area is cleansed in the same fashion as for subcutaneous injection. The 

 previously warmed material, free from air bubbles, is then slowly injected. 

 As the needle is withdrawn, alcohol-soaked cotton should be pressed over 

 the puncture until the bleeding stops. The following needle sizes are 

 suggested for general use: mice, 27-gauge; rats, 25-gauge; guinea pigs, 

 25-gauge; rabbits, 23-gauge; larger species, depending upon the size. 



Intraperitoneal. This route permits of simple inoculation of relatively 

 large volumes of material, and because of the rapid absorption of sub- 

 stances from the peritoneum, it provides tissue saturations only slightly 

 slower than in the case of the intravenous. The area is disinfected as 

 before, and the needle passed through the skin and then through the 

 abdominal wall with a short stabbing motion. Care should be taken to 

 avoid puncturing the viscera, and this danger can be minimized by 

 injecting into one of the lower abdominal quadrants. 



Intrapleural. This procedure is the same as for intraperitoneal injec- 

 tion except that one injects into the pleural cavity anterior to the dia- 

 phragm. The actual point of inoculation depends upon the experimental 

 animal. The intrapleural route is usually employed for the purpose of 

 obtaining exudates, and additional details of the procedure can be found 

 in the standard bacteriological texts. 



Per OS. Introduction of the material into the stomach or intestines 

 may be readily accomplished by means of a catheter or capsules or by 

 mixing the inoculum with food or drink. To avoid exposure to the gastric 

 juices the material may be closed in enteric-coated capsules. Liquids 

 may be mixed with starch and made into pills which are readily digestible. 

 In the case of mice and rats it is simplest to blunt the end of a 19- or 

 21-gauge needle by grinding it down and then passing it gently into the 

 esophagus while holding the rodent vertical and retracting the head to 

 provide a relatively straight passage. 



