VARIATION OF SALMONELLA PULLORUM 53 



of infected birds, often as few as one. Cultures obtained from adult birds and 

 studied in this investigation represent positive isolations irom flocks revealing 

 only one infected bird. Some of these infected individuals possessed very low 

 agglutinin titres, which may be due in part to the organism. In order to obtain 

 more evidence which might serve to explain the relation of bacterial variation to 

 flocks revealing one or more infected birds, a specially designed project seems 

 necessary. 



Environment and Bacteria 



The placing of bacteria under different environmental conditions may bring about 

 many types of variation in the organism. The observations reported in this 

 investigation are in general agreement with those reported for other organisms. 

 While it may be true that 5. pullorum is quite stable when maintained under 

 uniform and constant laboratory conditions, under certain influences such as 

 described earlier, the organism may undergo profound changes. The majority 

 of strains studied were susceptible to marked variation. It was impossible to 

 study slight variation simultaneously with extreme changes, but the author 

 feels that this phase is probably of great practical importance. Slight variations 

 from the normal type are more difficult to detect, and they may be induced by 

 unfavorable environment. Various strains will respond differently to the same 

 environment. This has been observed when strains were streaked on liver infusion 

 agar. Differences in colony and cellular morphology may be noted. This also 

 holds true for agar medium prepared from different livers. Liver medium may 

 serve to bring out variation tendencies that otherwise might remain obscure. 

 The results suggest that continuous cultivation of S. pullorum on liver infusion 

 medium is more liable to bring about a change in the organism than growth on 

 plain meat extract agar. 



The relation of one colony type to another cannot be explained with any degree 

 of satisfaction. It appears that certain types are more remote from the parent 

 strain than others, but this may be applicable only to one or more features, such 

 as colony form, virulence, and antigenic structure. To classify all of the different 

 variants as to their order of development or degree of variation does not seem 

 possible at this time. The realm of variation may possess great latitude. The 

 border between normal and variant types should not be looked upon as a sharp 

 line of demarcation. A normal type may vary in some of its aspects, but the 

 changes may not be perceptible. Furthermore, a normal type may lose one prop- 

 erty which is replaced by another characteristic as, for example, smoothness for 

 roughness in colony surface. The change from the smooth to the rough character 

 may extend over a wide range of colony types. Also, a character may completely 

 disappear without the acquisition of a new property, as, for example, the loss of 

 ability to ferment a certain carbohydrate. Additional properties may be acquired 

 without previously having lost a character, as is the case with the maltose ferment- 

 ing strain included in this investigation. One and the same type of variant may 

 appear different on two kinds of media. Variants may fluctuate in their colonial 

 and cellular types. Colonies that consist largely of the filamentous forms are the 

 most difficult to propagate and to maintain as stable. However, Variant XII-b,« 

 which produces a filamentous type of colony, has remained very stable and 

 uniform in its features. 



The terms "S" and "R" introduced by Arkwright for smooth and rough 

 forms seem most inappropriate, because variants may be observed which have 

 a smooth surface and yet are far remote from the parent strains in antigenic 



