200 STRONG AND TEAGUE. 



37 °C. agglutinates at much greater dilutions of the same immune 

 serum than does the previous strain when grown at this same tem- 

 perature. Furthermore, the differences in agglutinability before 

 and after passage through an animal are more marked. 



The strain of Table V, when grown at 37° C, agglutinates at 

 still greater dilutions. When cultivated at 32° C, flocculation 

 takes place almost as quickly with normal serum as with immune 

 serum, and it is difficult to decide whether or not specific agglu- 

 tination has taken place. 



Our strain of avirulent plague may be cited as the extreme of 

 this series, showing varying grades of agglutinability. Even 

 when cultivated at 37°C., spontaneous sedimentation takes place 

 so rapidly that it is impossible to say that specific agglutination 

 has occurred. Although this strain was used in producing the 

 immune serum, we have in no single instance been able to 

 show that it was agglutinated specifically by the serum. 



The same immune serum was used for the tests recorded in 

 Tables III, IV, and V. 



We have previously noted that the plague bacillus forms more 

 mucus when cultivated at 37 °C. than when grown at 32° C. or 

 even lower temperatures and that more homogeneous and more 

 durable suspensions result in the former instance. We now see 

 that the bacillus when grown at 37 °C. is agglutinated with 

 greater difficulty by a specific serum. It, therefore, seems not 

 unlikely that the decrease in agglutinability is due to the increase 

 in mucus production. In harmony with this view is also the 

 fact that strains freshly isolated from experimental animals 

 produce more mucus and are less readily agglutinated by a spe- 

 cific serum than are strains which have been cultivated for 

 months upon artificial media, though the factor of possible dif- 

 ference in virulence also must be considered in this instance." 



Finally, we may add that during the course of these exper- 

 iments we have been able to identify promptly by the agglutina- 

 tion test two strains which were isolated from bubonic cases of 

 plague dying upon ships in the harbor of Manila. 



While one of the difficulties in the performance of the agglu- 

 tination test with the plague bacillus is the tendency toward spon- 

 taneous flocculation, we are inclined to believe that, under proper 

 conditions, spontaneous flocculation usually does not occur in 

 freshly-isolated strains; in most strains which have been grown 

 upon artificial media for long periods of time it can be avoided by 



= Strong, Journ. Exp. Med. (1905), 7, 229. 



