DOWNS: BACILLUS TYPHOSUS. 163 



Trowbridge (12) reports the occurrence of a typhoid epidemic 

 among vaccinated persons in an institution. Here • the original 

 source of infection came from the milk supply, which was infected 

 by a vaccinated worker with a mild case of typhoid. It is realized 

 that in such an epidemic the dosage may have been sufficient to 

 overcome the innnunity acquired from vaccination. Wade and Mc- 

 Daniel (13) report the occurrence of an epidemic in an institution 

 among vaccinated individuals. Here there seemed to be an in- 

 teresting correlation between the negative Widals given after vac- 

 cination and the susceptibility of these persons to typhoid. Myers 

 and Nielson (6) report the isolation of an atypical strain of typhoid 

 from the blood stream and stool, respectively, of two vaccinated 

 persons. 



Hooker (9) and Weiss (2) conclude from their experiments that 

 a vaccine made from several strains of typhoid would be more effi- 

 cient than one made from a single strain. The results of these ob- 

 servers and the others reported, together with our findings, would 

 suggest that at least it might be well to consider the use of a vaccine 

 made from several strains. 



Stober (14) reports three negative Widals and seven positive 

 Widals, using an organism isolated from urine. Mock (11) also re- 

 ports negative agglutination with typical typhoid organisms iso- 

 lated from clinical cases. Robinson (15), on the other hand, re- 

 ports no variability in 100 Widals using the Worcester and Raw- 

 lings strains. 



In summing up the work done the following conclusions may be 

 drawn : 



1. Culturally, the typhoid organisms studied differ very slightly 

 from each other, the reaction being most variable in dextrine, 

 xylose, salacin and litmus milk. These variations cannot be cor- 

 related with the age of the culture nor source. 



2. Cross-agglutination and absorption tests establish the exist- 

 ence of at least quantitative antigenic differences between the 

 strains used. It occurs to the author that the conflict as to whether 

 there are antigenic differences in the typhoid group, may be due to 

 the fact that qualitative rather than quantitative differences have 

 been emphasized. 



3. There is a marked difference in the agglutination of organisms 

 with the sera used in Widals, and it would be advisable to set up 

 each Widal with more than one strain, selecting strains which were 

 known to give a high percentage of positives. 



