THE DETECTION OF BACTERIAL PATHOGENICITY 231 



shaving or depilation should be avoided. Following inoculation the site 

 may be covered with sterile cloths or coated with collodion to exclude 

 air. However, the latter procedure may create a degree of anaerobiosis, 

 and this makes the conditions abnormal. It is sometimes desirable in 

 cutaneous inoculation to abrade the epidermis by scratching or scraping 

 with a sharp instrument. A small piece of tin similar to that used when 

 vulcanizing a rubber tire tube can be employed for this purpose. Scrap- 

 ing aids penetration by removing the outer defensive epithelium and is 

 similar to intracutaneous injection. When very small amounts of 

 inoculum are available, it is sometimes necessary to resort to the latter 

 type of inoculation. 



Intracutaneous. By intracutaneous injection is meant the introduc- 

 tion of material into the epithelial layers. The formation of a bleb during 

 inoculation indicates successful injection. It is advisable to use animals 

 with a nonpigmented skin, and rabbits should not be in molt. Shaving 

 and the application of antiseptics may interfere with making a test and 

 should be used judiciously. A 25- to 27-gauge needle is used and, with 

 the bevel uppermost, is inserted at a slight angle to a depth sufficient only 

 to cover the bevel. Pressure should be maintained on the needle during 

 inoculation, and the maximum permissible quantity is about 0.1-0.2 ml. 



Subcutaneous. This is one of the most common routes of inoculation 

 and adaptable to a wide range of pathogens. The skin may be shaved or 

 the hair clipped or plucked without interfering with the procedure. 

 Material should be injected into the subcutaneous tissue and, when per- 

 formed on the abdomen, with care not to puncture the peritoneal wall. 

 The area may be disinfected with a nonirritating disinfectant, such as 

 tincture of zephiran chloride, alcohol, merthiolate, or green soap. The 

 area of injection may be marked with an indelible pencil. The size of 

 the needle and the amount inoculated will depend upon the material and 

 the animal. A 21- to 25-gauge needle and volumes up to 2 ml are 

 customary. 



If the material will not pass through the needle, as in the case of thick 

 bacterial suspensions, adjuvant preparations, or certain toxoids, the skin 

 may be sterilized, after removal of the hair, and a V-shape opening cut 

 into the skin with sterile scissors or a sharp scalpel. The flap is then 

 lifted up and loosened until a pocket is formed into which the material to 

 be injected is inserted. After the flap is replaced, the area is steriUzed 

 and covered with collodion or aseptically sutured. 



Intramuscular. The skin is treated as for subcutaneous injection, but 

 the inoculum injected deep into the muscle. Be certain to use a needle 

 of adequate length. With larger animals it is good practice to withdraw 

 the syringe plunger before injection to make sure that the point of the 

 needle has not accidentall}?- entered a large vessel. 



