234 MANU/^.L OF MICROBIOLOGICAL METHODS 



and become embedded in the opposite wall. The presence of the needle 

 point in a cardiac chamber is usually indicated by the appearance of 

 blood in the syringe. The inoculum must be injected slowly, or the 

 animal may go into syncope. 



THE CARE OF EXPERIMENTAL ANIMALS 



It must always be borne in mind that unknown agents and many 

 known infectious materials may be dangerous. It is the responsibility of 

 the person who inoculates animals to ensure that everyone coming into 

 contact with these animals does not inadvertently run a risk of infection. 

 Unless there is a vaHd and specific reason to do so, it is ill-advised to 

 inoculate animals unnecessarily with certain agents, e.g., anthrax or 

 tularemia. A large forceps and container of suitable germicide should 

 be kept in the animal area, and sick or dead animals handled with these 

 forceps, especially when being removed from the cage. In many labora- 

 tories gowns or laboratory coats and a suitable type of face mask must be 

 donned before entering the area of infected animals. This is particularly 

 important in the case of tuberculosis and the mycotic diseases. When 

 sick animals are to be disposed of or it is desired to sacrifice them for 

 autopsy, they may be killed by dropping them into a suitable chloroform- 

 filled container. This same container should not be used for the anes- 

 thetization of healthy animals. The disposal of infected carcasses is best 

 accomplished by incineration, and waterproof disposal bags are now com- 

 mercially available which serve as excellent containers for transportation 

 of animals to the incinerator. All animal quarters should be kept scrupu- 

 lously free of arthropods, especially when such agents as Pasteiirella pestis 

 are being studied. 



CLINICAL SIGNS IN ANIMALS 



Certain types of clinical signs are readily recognizable and, with 

 increasing experience, will be found to provide a valuable guide to the 

 health of the animal. However, all too frequently a sick animal will be 

 found to be showing symptoms which are not caused by the injected 

 material but rather by such unforeseen circumstances as starvation, 

 thirst, spontaneous tumors, etc. Furthermore it should be remembered 

 that the same microorganism may cause a different disease picture, 

 depending upon the organs which are involved. 



In mice a hunched back and quiet position in the cage may signify 

 gastrointestinal infection or a systemic disease. Central nervous-system 

 lesions may cause tremors, rolling, ataxic gait, or a tendency to jump 



