﻿242 STRONG. 



agglutinative reaction of supposed plague immune sera., I have occa- 

 sionally encountered pseudo-agglutinative reactions in the control tubes 

 containing normal serum and suspensions of plague bacilli, which 

 could not be distinguished from those of true agglutination. In the 

 tubes in some instances were seen typical, flocculent precipitates, visible 

 to the naked eye and which settled to the bottom, leaving the overlying 

 liquid clear. Such reactions occurred at the same time in the same 

 dilutions of the immune serum which was being tested, but not in 

 the test tubes containing the suspensions of bacilli alone, and hence 

 if the control tubes with normal serum had not been prepared, the 

 reactions unquestionably would have been considered as true agglutinative 

 ones, which they certainly were not. It is true that the precipitation 

 obtained in these instances disappeared to a greater or less extent on 

 shaking the tube and it then re-formed slowly, but notwithstanding 

 statements in the literature to the contrary, the same phenomenon 

 (disappearance of the precipitation on shaking) occurs in the true agglu- 

 tination not only of plague but also of cholera, and certain other micro- 

 organisms. 



From what has been said above it is evident that the time limit for 

 the completion of the agglutinative reaction of the plague bacillus is very 

 important. Most observers have limited the time of the reaction to 

 within two hours. However, Shibayama, 00 who concluded that 72-hour 

 cultures of the plague bacillus, cultivated in the ice box, are agglu- 

 tinatined in much higher dilutions than are the same strains grown 

 at 32° to 37° C, drew his conclusions from an examination of the 

 reaction after twenty-four hours. In this connection I here shall record 

 some recent experiments performed with two sera obtained from monkeys 

 which had been immunized against plague and with one serum from, a 

 normal monkey. The agglutinative values of these three sera were tested 

 in dilutions of 1 to 10 and 1 to 20, first with 72-hour cultures of a 

 virulent pest strain which had been cultivated for six generations in 

 the ice box at a temperature of from 5° to 10° C. and second with 

 48-hour cultures of the same strain cultivated for the same number 

 of generations at 30° C. The readings of the reactions were made after 

 one and one-half hours and were all found to be negative, no traces 

 of agglutination appearing in any of the tubes. After sixteen hours 

 the tubes were all examined again. At this time in those containing 

 the suspensions which were made with the bacteria cultivated at 5° to 

 10° C. there was almost complete precipitation of the organisms, the 

 overlying liquid being clear in all, including the control tubes with 

 normal serum and those containing suspensions of the bacteria in saline 

 solution with no serum, as well as the tubes with the immune sera. 

 In the tubes which contained the serum and suspensions of the organisms 



66 Log. cit. 



