DETERMINATION OF THE PATHOGENICITY OF AEROBES vir4s-9 



organisms contaminating the cultures (Heith, 1926). Elliott (1938) 

 claimed that lysis of erythrocytes and leucocytes by saponin in- 

 creases the number of positive cultures when few bacteria are present. 



The presence and type of antibodies for the organism recovered 

 should be determined, particularly if the animal does not die. Recov- 

 ery without the development of antibodies suggests that the organism 

 recovered may not have been the cause of the infection but may have 

 been a temporary invader which disappeared without stimulating 

 much antibody production. If the animal dies, antibodies probably 

 will not be present to any extent but if at all will be most intense just 

 before death. Therefore, blood should be drawn immediately after 

 death. Antibodies do not indicate pathogenicity, but they are sup- 

 porting evidence. 



Autopsy 



The following should be determined at autopsy The cause of 

 death; the type and distribution of the lesions; any cellular changes; 

 distribution of the infecting organism; changes that may have taken 

 place in the microorganism; and whether antibodies are present. 



Natural infection may interfere wdtli animal experimentation; 

 hence, the autopsy should be made immediately after death to reduce 

 terminal invasion. If the autopsy cannot be made promptly the 

 body should be kept in the refrigerator. The autopsy should be 

 done in a good light with instruments that have been sterilized by 

 dry heat or in the autoclave. 



The animal should be prepared by wetting the hair with a disin- 

 fectant that penetrates to the skin. Wetting with alcohol first helps 



Examine the area of the injection. Open the animal down the 

 median ventral line and pull the skin back. Cover all but the 

 exposed area with towels moistened with the antiseptic. Search for 

 gross lesions, remove suspicious glands, tissues, etc. and place them in 

 Petri dishes for culture and histologic examination. Moisten the 

 exposed surfaces with alcohol and ignite. 



Open the pleural cavity with a fresh set of instruments, taking care 

 not to cut the diaphragm or pierce the lungs. If desired, seal a 

 sample of the pleural fluid in a capillary tube and store it in the 

 refrigerator for cytological and cultural study. Make smears and 

 cultures of exudates. If the animal died from an infection, the 

 organism will be abundant in most of the body fluids, and a small 

 amount, such as a loopful, of each will lessen the chance of recovering 

 contaminants. 



Open the pericardium and sear the surface of the heart. Make an 

 incision with a sterile instrument and proceed as with the pleural 

 exudate. 



The lungs may then be examined and any cultures or sections made. 

 Peripheral blood may be compared with the heart blood. The blood 

 and other body fluids may be tested for antibodies, but if the infection 

 was of short duration they may not be detected. A high titer of 

 antibodies for the organisms recovered suggests that they may not 

 have caused death but this is not necessarily so because in diphtheria, 

 e.g., the appearance of antibodies may be followed by improvement 

 and yet the animal may die from liberated cardiotoxins. 



