VARIATION OF SALMONELLA PULLORUM 43 



Lot IV. The chicks inoculated with Strain I and its variant C responded in 

 the same manner as those in Lot I, in spite of the fact that they had been chilled 

 while those in Lot I had not. It appears that these two strains, as employed 

 here, might be considered avirulent. Strain XIV and its variant E behaved simi- 

 larly, although the parent strain appeared slightly more virulent. However, this 

 difference may not be significant, since the clinical and pathological manifesta- 

 tions may be due in part to other factors, aside from virulence. The strains isolated 

 resembled the original inoculated type. 



Lot V. The strains employed in this lot produced negative results in every 

 respect. As a matter of interest, ten chicks from this lot were inoculated with 

 variant XH-b. Positive isolations of this variant were obtained. (These results 

 are reported in Experiment 4, page 39.) 



The chicks employed in subsequent lots were received from a different source. 

 Unfortunately, one infected adult bird was detected in the parent stock from 

 which the chicks in the previous experiments were obtained. This flock had not 

 harbored birds reacting to the macroscopic agglutination test, for three years. 

 However, the chicks received from this flock did not represent the progeny of the 

 infected bird or birds that were in contact with the latter, and it appears from the 

 results that the chicks employed undoubtedly were free from the disease. 



Lot VI. Most striking results were obtained with the strains in this group. 

 Strain VIII was observed to be markedly virulent, as compared to its variant 

 and other strains employed previously. All chicks died within two days after 

 inoculation. No symptoms were observed in the chicks that were inoculated with 

 the variant. 



Lot VII. In this group the type of variant was similar to Vlll-a used in Lot 

 VI. Strain III-S represents a typically smooth strain selected from the same 

 "SR" culture from which Ill-a was derived. Strain III-S had been treated in the 

 same manner as Ill-a and was included in this lot to determine whether the 

 decrease or loss in virulence might be due to the treatment of the organism which 

 affected virulence only, or whether the difference in colonial appearance rep- 

 resented certain profound changes in the organism which also influence virulence. 

 It was observed that the symptoms, mortality rate, and lesions were quite similar 

 for Strains III and III-S. One chick inoculated with Ill-a died from overcrowding. 



Lot VIII. In this lot an effort was made to determine the influence of diluting 

 the concentration of the dose used for inoculation. The parent strain was prepared 

 in two different concentrations, the one equal to the usual turbidity employed, 

 and the other diluted three times. It may be observed that there were no noticeable 

 differences in the results of the inoculations. Also, two groups of five chicks each 

 were inoculated with Variants Vlll-a and Ill-a, respectively, for five consecutive 

 days. No symptoms were detected in the chicks inoculated with the variants. 



Lot IX. Two variants derived from one and the same strain were employed 

 in this lot. The parent strain caused mortality, and the number of positive isola- 

 tions of this strain was greater than that of the variants. Variant XH-a was 

 isolated as typical 5. pullorum, but Xll-b was recovered with apparently little 

 or no change in colonial and cellular morphology. (See Figures 18, 64, and 65.) 



Lot X. In this group XII-S was a smooth strain which was derived from XH-a 

 ten days prior to inoculation. While the difference in symptoms, mortality, and 

 lesions between the parent strain and the two variants is marked, the two variants 

 behaved quite similarly. It appears that, although the property of smoothness 

 had returned, the virulent property of the parent strain had not been restored. 



