64 



o. rsHii 



In performing this test, therefore, I have found it convenient 

 to grow each strain (6 or more) of this organism in broth medium 

 at 37°C., for eighteen to twenty hours. Formaliu 0.1 per cent 

 is added to each of the cultures, which are then all mixed to- 

 gether, and are ready for immediate use; or they may be stored 

 in a cold room until needed, as m Dreyer's method. This prep- 

 aration gives reliable results in diagnosis with an unknown 

 serum. 



TABLE 13 

 The serum of typhoid fever, Widal test with different strains 



Key: 5, complete; 4, almost complete; 3, weak; 2, very weak; 1, trace; 0, 

 negative agglutination; +, positive reaction. 



SUMMARY 



1. Formalin 0.05 to 0.2 per cent prevents spontaneous agglu- 

 tination almost entirely in some instances and entirely in others 

 with Bad. iyphosum and Bad. paratyphosum A and in a lesser 

 degree with Bad. paratyphosum B; with Bad. coli formaUn has 

 no effect in this regard. 



2. One-tenth per cent formalin prevents spontaneous agglu- 

 tination and increases specific agglutination, ha\'ing a strong 

 effect on Bad. typhosum and Bad. paratyphosum A, but less on 

 Bad. paratyphosum B and Bad. dysentenae and none on Bad. 

 coli. 



3. Formalin prevents pseudo agglutination to a great extent 

 in cross agglutination test with different sera. 



4. Cultures in acid medium in which there is heavy growth 

 and active motiHty, yield stronger agglutination than cultures 



