34 MASS. EXPERIMENT STATION BULLETIN 319 



with the normal smooth type. In Table 7 it may be observed that three variants 

 with a rough colony type did not change at any time to the extent that the 

 colony type resembled the smooth form. The four remaining variants exhibited 

 some degree of fluctuation in their colony morphology. (See Figures 12, 16, and 

 23.) Two parent strains (I and XIV) also manifested a variation in colony type. 

 However, as mentioned earlier, these two strains cannot be considered as stable, 

 normal types. According to the results obtained, one is led to believe that the 

 colonial morphology of variants and typical, smooth strains seems to be affected 

 but slightly when cultivated in whole fresh eggs. This observation may have a 

 very important bearing upon current methods of preserving antigen stock cultures. 

 It would seem that the change in environmental conditions for this organism may 

 not be so great in the egg as in agar slope cultures maintained at different tempera- 

 tures. 



At the time of three different transfers (tenth, eleventh, and fifteenth), the 

 growth from the streaked plates was placed in different concentrations of NaCl 

 solution in order to determine the stability of the organism in suspension. Table 

 8 shows that all variants exhibited some degree of salt sensitiveness. Three strains, 

 among the typical group exhibited a slight degree of instability. However, two 

 of these strains (I and XIV) are erratic in their behavior and almost always will 

 pass for typical, smooth types. From the results given in Table 8, it appears 

 that little or no change occurred in the behavior of any of the strains in NaCl 

 solution following frequent transfer and cultivation in whole egg. 



Table 8. — Influence of frequent transfer in fresh eggs on the cellular 

 stability of 5. pullorum AS revealed in saline solutions 



The cultivation of variants in fresh egg yolk placed in sterile tubes did not 

 prove as satisfactory as the whole-egg method for maintaining the different 

 types. The egg yolk-tube method is objected to for the reason that the yolk 

 undergoes desiccation, a change in composition, and, in all probability, an altera- 

 tion in appearance. Environmental factors seem to exert a greater influence in 

 the egg-yolk than in the whole-egg method. Considerable difficulty was encoun- 

 tered in keeping the variants viable during their sojourn in the yolk. In a few 

 instances an incubation period of two weeks was sufficient to cause death. Also, 

 this method involves a greater risk of contamination. The organism apparently 

 attacks the components of the yolk material, since the inoculated tubes differed 



