212 ORIENTAL PLAGUE chap. 



dilution of 1 in 20, this agglutination taking place within 

 the half-hour. 



As will be presently described, the agglutination test 

 has been made in a considerable number of cases of 

 protected animals, and as a result it has been found that a 

 dilution of 1 in 20, left at rest for half to one hour, is a 

 fair standard and index for deciding one way or another. 

 In the first place, I found that if, in a given instance, the 

 agglutination test was positive with a dilution of 1 in 20 

 within the half-hour, it was positive also at 1 in 30 within 

 the hour, but doubtful with 1 in 40 within the hour ; 

 and, on the other hand, that if the agglutination test was 

 negative at 1 in 20 within the half-hour, it was equally 

 negative at 1 in 10, or less, dilution within the half-hour. 1 

 In all the statements to be made here the test was 

 declared positive if in dilution of 1 in 20 distinct 

 clumping was observed within the hour in a preparation 

 made in the manner of the hanging drop. 



I. — Experiments of Agglutination with Blood 

 of Guinea-pigs 



1. Gui7iea-pigs 1 and 2. — (a) These two guinea-pigs 

 were injected, February 18, with a salt emulsion of the 

 laboratory B. pestis, 2 scraped from the slanting surface of 

 an agar culture. The emulsion was thick and strongly 

 turbid, and had been sterilised at 70° C. for fifteen minutes. 

 Cultures made after the sterilisation did not yield any 



1 Dr. Markl's observations, Centralbl. f. Bakteriologie, etc., p. 810, vol. xxix., 

 N. 21, lose a great deal of their value because he uses dilutions as low as 1 : 2, 

 1 : 5, and speaks of twenty-four hours' duration. 



2 In all experiments described here and subsequently the strain of plague 

 bacilli was one derived from a case of plague pneumonia that had occurred in 1896 

 in the London Docks (L.P. I.). 



