36 MASS. EXPERIMENT STATION BULLETIN 319 



the variants the reader should refer to Table 4. Saline suspensions were prepared 

 from 24-hour cultures, and the turbidity was standardized to tube 2 of McFar- 

 land's nephelometer. Each chick was given 0.1 cc. of the bacterial suspension 

 per orem. During the first seven days after exposure no symptoms were observed, 

 and there was no mortality. It was deemed advisable at this time to expose the 

 chicks a second time in order that positive isolation might be obtained. Hence, a 

 second dose (0.5 cc.) of a suspension similar to the first was administered sub- 

 cutaneously. In Table 10 are given the results obtained from the two exposures 

 to infection. 



Table 9. — Results of feeding 5. pullonim variants to young chicks. 



Strain Number Number Number Number Number 



No. of Died Yielding Killed Yielding Remarks 



Chicks S. pullorum S. pullorum 



11706* 5 2 2 2** 2 Symptoms and lesions observed 



Typical S. pullorum recovered 



No lesions observed 



Few lesions observed 



Feu lesions observed. The re- 

 covered organism resembled 

 the original variant 



4 No lesions 



♦Represents a normal strain. 

 ♦♦Unfortunately, one chick from group 11706 escaped to cage D-l on the day the chicks were 

 necropsied. The organism isolated from Group D-l resembled 11706 more closely than D-l; hence 

 it may be that the escaped bird was infected with strain 11706 and that all birds in Group D-l 

 were negative. 



It is apparent that a greater mortality was encountered from the smooth 

 typical strains than from the variants. Likewise, the percentage of positive isola- 

 tions of S. pullorum was far greater among the typical strains than among the 

 variants. Among the latter, three strains (C, D-l, and IX-b) failed to produce 

 infection. 



Variant B (Table 10) established itself in six of seven chicks. In most instances 

 necrotic foci were observed in the liver of these chicks. Prominent fibrous nodules 

 were detected in the myocardium, wall of the proventriculus, gizzard, and intes- 

 tine. This type of lesion was observed in one or more organs in every chick in- 

 oculated with this strain. S. pullorum was isolated from the majority of tissues 

 cultured. In a few instances the colony form on plain meat extract agar revealed 

 a slight tendency toward roughness, but these rough features were more pro- 

 nounced in cultures isolated on liver infusion agar. (See Figures 31-37, inclusive.) 

 Stained smears prepared from colonies on plain meat extract agar revealed typical 

 cells, while those prepared from liver infusion agar contained markedly pleo- 

 morphic types. (See Figures 38-41, inclusive.) The cells were also larger in 

 smears prepared from colonies on liver infusion agar. The results obtained with 

 Variant B clearly show that the organism had lost some of its original features 

 during its passage through the host. However, it also is apparent that the re- 

 covered organism is not typical in every respect, as shown by the colonial and 

 cellular morphology. 



Variant E (Table 10) was recovered from two chicks. One of these died within 

 twelve hours after inoculation. Upon necropsy no significant gross lesions were 

 observed. The organism was recovered from the liver and spleen. On plain meat 

 extract agar the growth resembled that produced by this organism before injec- 

 tion. On liver infusion agar typical rough growth was detected. (See Figures 

 42 and 43.) 



