VII48-10 MANUAL OF METHODS FOR PURE CULTURE STUDY 



Open the peritoneal cavity with a new set of instruments. Treat 

 the peritoneal exudate like the pleural exudate. Sear the surface of 

 the liver, spleen, kidney, etc. for cultures and store pieces for patholo- 

 gical study where indicated. 



Examine all the organs, joints and cavities and make cultures 

 where indicated. In cultures of the brain take samples from different 

 regions to determine the distribution. 



Smears made at autopsy should be stained for Gram reaction, 

 capsules and spores. 



Factors Interfering with the Determination of Pathogenicity 



Factors interfering with the determination of pathogenicity were 

 described by Teale (1933). Unless they are taken into considera- 

 tion, they may lead to erroneous conclusions. An organism or its 

 products may affect only one part of the body, and this in a specific 

 manner, while other organisms may attack any part of the body 

 and produce a variety of disease conditions. Different organisms 

 may attack the same part and produce similar changes. 



A pathological change in the animal tissues produced by the injec- 

 tion of an organism or its products indicates pathogenicity but con- 

 trols must be used to exclude other factors. The ability to grow in 

 or upon animal tissues or fluids is not of itself evidence of pathogenic- 

 ity. Finally, non-pathogenic organisms may produce serological 

 and other changes. 



Variations in the resistance of individual animals or strains must 

 also be taken into account. (As by Gumming, 1943). Infection 

 may occur when an individual of low resistance is injected even with a 

 normally non-pathogenic strain. Hence, several animals should 

 always be used in tests of pathogenicity. 



The following factors also interfere with the determination of 

 pathogenicity : 



Variations in the bacterial mass. Bacterial cells, like other biologi- 

 cal units, vary around a mean because the transmission of different 

 characters is imperfect. To reduce errors from this source it is 

 desirable to use a culture prepared from several colonies. The cells 

 vary with age, both naturally and in response to the environment, 

 the latter as temporary adaptations or non-adaptative changes 

 which may be transmitted through successive generations and then 

 disappear. The changes rarely result in mutations. Holman and 

 Garson (1935) discussed precautions that must be observed in the 

 study of bacterial variation. 



Natural variations. Natural or normal variations include varia- 

 tions of individual cells around the mean and variations resulting 

 from the life cycle which may vary in all the morphological, physio- 

 logical and pathogenic properties of the culture. Selective cultiva- 

 tion and animal passage of cultures that have lost pathogenicity 

 may lead to development of pathogenic cells in the culture. Some 

 non-pathogenic cultures may contain pathogenic variants, parti- 

 cularly if the culture was associated with a disease process. Hence, 

 the advisability of testing a number of colonies separately. 



