136 NOTE [vol. 59 



that the culture was not flocculated by S. paratyphi A serum (a) but reacted 

 with serum derived from the "nonspecific" phases of the genus (1,2: 1,5: etc.). 

 When tested for single factors 2, 3, 5, 6, and 7, it was agglutinated only by 5 

 serum. In absorption tests it removed all agglutinins from serums prepared from 

 1,5 phases of S. paratyphi A. Thus the culture was identical with the 1,5 phases 

 previously induced by growing S. paratyphi A in homologous serum. 



The culture was monophasic and was immobilized when placed in semisolid 

 medium to which had been added various 1,5 serums. After repeated transfers, 

 bulbs extending from the site of inoculation appeared. When these bulbs were 

 transferred to additional tubes of the same medium, the culture migrated rapidly 

 through the agar. From the spreading growth was isolated a form that was ag- 

 glutinated to 20 per cent of the titer of H serum of S. paratyphi A and that 

 reacted to approximately the same degree with serums produced from the 

 "artificial" phases z 6 and z n . When the culture was grown in semisolid medium 

 to which z 5 and Zn serums as well as 1,5 serum had been added, no spreading 

 occurred although the serums were carefully absorbed to remove interfering 

 factors and the organism was carried through a number of transplants extending 

 over a period of 6 months. It should be emphasized that it was very difficult to 

 cause reversion of induced 1 , 5 forms of S. paratyphi A to the original form and 

 that attempts to cause reversion failed in most instances. 



The observations outlined above provide the first report of the natural occur- 

 rence of phase 2 of S. paratyphi A having the antigenic formula I, II, XII: 1 ,5. 

 Such a variant is not, therefore, merely a curiosity produced by artificial manip- 

 ulation, although it was biochemically and antigenically identical with strains 

 developed by cultivation of typical cultures in agglutinating serums. The findings 

 emphasize further the importance of the study of phylogenetic and evolutionary 

 trends of the Enterobacteriaceae in the identification of aberrant cultures. 



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