VARIATION OF SALMONELLA PULLORUM 11 



and hydrochloric acid. This fraction, protein in nature, was extracted from "S", 

 "R", and "p" races of several Salmonella types. It was concluded that the "T" 

 fraction was more deeply situated in the organism than were the "S", "R", and 

 "p" receptors, and could engage with its universal antibody only when the 

 bacterial surface had been partly cleared of impediments as a result of washing, 

 or during autolysis. 



Henry (1933) observed that the "R" forms of Br. abortus exhibited less invasive 

 power for the natural host than the "S" type. This relation likewise was true 

 for agglutinogenic properties. Cultural examination of milk from reacting cows 

 in various stages of lactation revealed no "R" types. 



MacKenzie and Fitzgerald (1933) demonstrated qualitative and quantitative 

 alterations in agglutinative, absorptive, and agglutinogenic properties of Sal- 

 monella and Shigella strains. The antigenic behavior was found to vary indepen- 

 dently of colonial morphology and mode of growth in fluid media. The conver- 

 gence phenomenon was observed in which variants, derived from different species, 

 manifested serological identity. 



Rettger and Gillespie (1933) found that cellular morphology varied with the 

 medium employed and with the temperature and duration of incubation, in 

 working with B. megatherium. 



Stearn and Stearn (1933) in a series of papers referred to the fact that different 

 H-ion concentrations may cause various types of growth with the same organism. 



Murphy 2 in an attempt to induce variation in S. pullorum strains, observed 

 that the variants failed to remain stable and that reversion to the so-called 

 "normal" occurred on subsequent transfers. 



In a recent paper by Plastridge and Rettger (1934) virulence studies on S. 

 pullorum were reported. The strains employed were variants isolated from 

 natural outbreaks or derived in the laboratory. The test animals included chicks, 

 adult hens, rabbits and guinea pigs. Marked differences were observed in the 

 virulence of the individual strains of 5. pullorum for these animals. Some strains 

 were found to be highly virulent for both chicks and adults; others possessed a 

 low degree of pathogenicity for chicks, but were highly virulent for adult birds. 

 Some strains were relatively avirulent for both young and adult chickens. Pro- 

 nounced changes in virulence of some strains of S. pullorum were induced by the 

 action of bacteriophage. The passage of strains through the animals had, in 

 general, no appreciable effect on morphological, colonial, and agglutinative 

 characteristics of the variants studied. 



THE INCIDENCE OF VARIANTS AMONG NEWLY 

 ISOLATED STRAINS 



In the identification of 5. pullorum strains several properties such as colonial 

 and cellular morphology, Gram stain reaction, biochemical reactions, and sero- 

 logical response are studied. While this organism possesses certain features in 

 common with some of the other members of the Salmonella group, yet as a rule 

 it can be isolated and differentiated with ease. Associated with its cultural habits 

 is a considerable tolerance to fluctuation in environmental conditions without 

 leading to death of the microorganism. In spite of the fact that S. pullorum is 

 not as selective in its growth environment as some organisms, certain conditions 

 may bring about profound changes in one or more of its characters, as will be 

 discussed later. 



'Unpublished data (1933). 



