VII48-12 MANUAL OF METHODS FOR PURE CULTURE STUDY 



may sometimes be eliminated by growing the organisms on different 

 culture media. This would be simpler than by adsorbing immune 

 sera with a common antigen. 



Distinction should be made between adsorption of a foreign 

 antigen, change in the bacterial antigen and physical mixture of a 

 foreign antigen. The latter can be removed by thorough washing 

 with saline. In working with obligate parasites, particularly filter- 

 able forms, the difficulties are increased due to antigens present in 

 tissues. 



The occurrence of heterophile or non-specific antigens and anti- 

 bodies complicates the study of pathogens. Yeast and Klebsiella 

 fneiimoniae stimulate immunity to Type II pneumococci, injection of 

 sheep cells produces immunity to anthrax (Rockwell, 1933) and in- 

 jection of Salmonella pulloruvi stimulates antibodies against S. 

 schottmulleri, S. paratyphi, S. (Eberthella) typJiosa and Shigella dysen- 

 teriae. Therefore, the presence in the blood of antibodies for a par- 

 ticular organism is not of itself convincing evidence that the organ- 

 ism caused the infection or that it acted as the antigen. 



The number, nature and natural occurrence of non-specific anti- 

 gens, their relationship to phase variations and their distribution 

 should be determined. Methods for studying non-specific antigens 

 concern Leaflet VIIL 



Obligate parasites. Still greater difficulties are encountered in 

 determining the pathogenicity of obligate parasites. The direct 

 transfer of body fluids or tissues involves the objections just dis- 

 cussed. Also, two organisms or non-specific antigens may be present, 

 as in typhus fever, and the immune sera produced when the animal 

 tissues or fluids are used as antigens may contain antibodies for both 

 organisms, making serological evidence inconclusive. 



The presence of organisms in tissue or in the blood stream is not 

 necessarily evidence of pathogenicity or parasitism. Organisms 

 from different sources are continually entering the blood stream and 

 dead tissues may be present in living animals permitting non-patho- 

 genic saprophytes to flourish. For these reasons, the only indication 

 of pathogenicity in the case of obligate parasites consists of an ac- 

 cumulation of circumstantial evidence. Improvements in tissue 

 culture technic may provide a solution. 



Specificity. The pathogenicity of an organism may be confined to 

 a single species of animals, which stresses the importance of the 

 proper selection of an experimental animal. The designation of an 

 organism as pathogenic or non-pathogenic, etc. refers solely to the 

 animal and method used. 



Passage through one animal may result in reduced pathogenicity 

 for another. The pathogenicity of an organism for a different species 

 of animal should be tested w4th cultures grown on artificial culture 

 media for some time as well as with freshly isolated cultures. 



Synergism. Occasionally two organisms may grow together and 

 produce a pathologic condition whereas neither can do so alone. 

 Both organisms do not necessarily produce toxins and it is possible 

 that one of them may in no way contribute directly to the disease 



