230 MANUAL OF MICROBIOLOGICAL METHODS 



animals may be done by tattooing, particularly on the ear for rabbits ; by 

 the use of numbered metal ear tags; or by some suitable stain. For 

 albino mice and rats a saturated alcoholic solution of picric acid is often 

 employed. Ample supplies of feed and water are absolutely essential. 

 In the case of guinea pigs one should guard against an excess fluid intake, 

 as these animals easily develop severe diarrhea when given too much 

 water. Usually a daily feeding of greens, supplemented with ascorbic 

 acid, is adequate for guinea pigs. 



Infected animals should be inspected daily, not only to determine death 

 but also to ascertain the first appearance of any clinical symptoms. It is 

 not good practice to bring normal animals into the same laboratory where 

 one is performing bacteriological work. Whenever possible it is a better 

 policy to take the material to be injected from the laboratory into the 

 animal area, where a separate section can be equipped for inoculations 

 and autopsy. 



Animals which appear to be sick or mangy or have snuffles, diarrhea, 

 marked loss of weight, middle-ear (rolling) disease, or obvious tumors 

 should not be used for pathogenicity studies. New shipments of animals, 

 especially when they are received in a crowded condition, are best utilized 

 after at least a 24- to 48-hr period of rest in clean cages. 



METHODS OF INOCULATION 



Because most pathogens are able to produce disease in the experimental 

 host only when inoculated via a suitable portal of entry, it is essential that 

 the operator be familiar with the technical aspects of animal injection. 

 There are innumerable methods of inoculating animals, and most labora- 

 tories will be found to have modified the standard procedures in some 

 fashion that suits them best. However, the following general routes of 

 inoculation and procedures are discussed to provide the beginning worker 

 with a basis for acquiring his own training. 



Cutaneous. This route of inoculation is rarely used for bacterial infec- 

 tion. It is more common in the testing of certain viruses, such as those 

 of the herpes group. The term is a rather loose one and includes scratch- 

 ing the skin or covering the deposited inoculum with an adhesive patch. 

 In some instances the inoculum is placed directly upon the adhesive 

 patch, which is then attached to the skin. The precise method is deter- 

 mined by the object to be attained. The skin should be cleansed and 

 sterilized with an antiseptic that has brief action, as 70 per cent ethyl 

 alcohol. The hair may be removed by plucking or shaving. If it is 

 desired to determine whether or not an organism can penetrate the normal 

 skin, the material should be spread over a nonirritated area; therefore 



