414 The Philippine Journal of Science 1918 



occurrence was not noticed until the second week of the disease 

 and even then only in low dilutions of the serum. 



Although the recent work of Strong ^ and of Strong and Teague * 

 has reduced the technical difficulties, the fact remains that positive 

 agglutination of plague bacilli by the patient's serum cannot 

 be obtained in the first week of the disease, and, therefore, the 

 isolation of plague bacilli from the body of the patient is still 

 the only quick and safe method of plague diagnosis. 



Having utilized the technique devised by Teague, I have had 

 no difficulty in performing the agglutination test in plague. The 

 emulsion of plague bacilli, to be used for the test, was prepared 

 by suspending young cultures of virulent plague bacilli, grown 

 at 30 °C., in salt solution and filtering the suspension through 

 filter paper. No antiseptic was added nor heat applied. Serial 

 dilutions of unheated patient's serum were mixed with equal 

 amounts of bacterial suspension in small test tubes. Incubation 

 at 35°C. followed. Controls, consisting of serial dilutions of 

 normal human serum as well as bacterial suspensions without 

 serum, excluded any possible error which might have been 

 caused by spontaneous sedimentation of the bacterial suspension ; 

 while a parallel test with highly agglutinant serum facilitated 

 the reading of positive results. 



Altogether, 22 tests were performed on 15 patients, 11 of 

 whom were fatal cases and 4 of whom recovered. In the nega- 

 tive reactions, the duration of the disease at the time of examina- 

 tion ranges from two to six days. The nonfatal cases showed 

 slight agglutination from the sixth day on. From that day, 

 the agglutination titer of the serum was found to rise, and 

 the agglutinins persisted in the blood of convalescents up to 

 the seventh week of the disease." 



It must be borne in mind that the patients, who showed 

 positive agglutination, had been vigorously treated with anti- 

 plague serum. Nevertheless, in consideration of the low titer 

 of the curative serum (dilution 1:32, agglutination positive; 

 dilution 1 : 64, agglutination negative) , the rise of the agglutinant 

 power of the patient's serum in dilutions higher than 1 : 16 

 cannot be explained as wholly due to passive immunity, but 

 rather to active immunity arrived at on the principle of simul- 

 taneous immunization. 



'This Journal, Sec. B (1907), 2, 155. 

 'Ibid. (1912), 7, 194-201. 



' It is hoped that it will be possible to examine some of the survivors 

 for agglutination from time to time. 



