VARIATION OF SALMONELLA PULLORUM 29 



Another type observed on plain agar is that exhibited by variant XH-a. This 

 type apparently has not digressed from the normal to the extent that some others 

 have, and also shows a greater tendency to revert to the typical form. A character- 

 istic peculiar to this type is that the colony moves in mass when disturbed with 

 a needle. This characteristic may be due to the fact that the colony is small and 

 mound-shaped and that its internal structure contains filamentous forms. These 

 forms may serve as a reinforcement in retaining the colony in its entirety. An 

 apparently similar action by these filamentous forms may be seen in Xll-b, in 

 which the periphery is largely composed of filaments which exhibit a tenacious 

 property. Also in small colonies composed largely of filaments the entire mass 

 moves in toto. 



The different types of variants established on liver infusion agar show colonial 

 and cellular characteristics different from those observed on plain meat extract 

 agar. The liver agar apparently contains certain constituents that have an 

 influence on the colony appearance and cell types. It has been observed that 

 friable, fatty, yellowish-brown liver tissue will produce an agar that is lighter in 

 color than that obtained from a firm, dark brown liver. The growth on agar medium 

 prepared with the latter is not as abundant and butyrous in character as on the 

 other medium. The liver tissue may vary in composition and thus affect the 

 character of the growth. 



In two instances during this investigation a mucoid type of colony was observed 

 on liver infusion agar. Attempts to stabilize this type failed. 



Certain variants may develop to a very impressive size on liver infusion agar. 

 This has not been observed on plain agar, although the colony size may be marked- 

 ly larger than that of the normal type. It was also observed in most instances 

 that liver infusion agar greatly exaggerated any unusual features that were 

 slightly noticeable in colonies growing on plain agar. Hence, liver infusion agar 

 may serve in some instances to determine the normalcy of a strain, or at least 

 bring out certain characteristics that may not be demonstrable with the ordinary 

 media. The continuous cultivation of 5. pullorum in liver infusion media may in 

 some cases lead to temporary variation and possibly permanent change in one or 

 more characteristics. A temporary variation was observed in one strain after 

 having been cultivated on liver infusion agar for a period of some months. The 

 mucoid type of colony also occurred spontaneously on liver infusion agar. Cellular 

 types produced on this medium do not resemble the normal types, especially in 

 the first transfer. With the organism capable of producing such responses on liver 

 infusion agar, it appears that an antigen prepared from liver cultures may be 

 expected not to react in the same manner as that prepared from a meat extract 

 agar growth. 



BEHAVIOR OF VARIANTS IN DIFFERENT ENVIRONMENTS 



Numerous investigations, reviewed by Hadley (1927), show that organisms 

 may lose or gain more than one property when undergoing variation. This 

 process does not necessarily involve certain characteristics, but it appears that 

 some properties are more frequently altered than others. Colonial and cellular 

 morphology, and pathogenic and serologic properties seem to be most susceptible 

 to change. Fermentative and other biochemical characteristics do not change 

 so readily. 



The variants in this investigation were studied as to their behavior in (1) 

 broth, (2) NaCl solution, (3) fermentable substances, (4) fresh whole egg and 

 egg yolk, and (5) the natural host. 



