210 ORIENTAL PLAGUE chap. 



there occurred the well-known discoloration of the fluid 

 (washing out of the haemoglobin of the blood corpuscles), 

 in consequence of which the blood became laky and only 

 the discoloured stroma of the blood discs was left. The 

 agglutinated masses of the plague bacilli in the mixture 

 were seen to be especially associated with the discoloured 

 stromata of the blood discs. A comparative experiment 

 made with blood of a normal rabbit (as also with blood of 

 normal guinea-pig, normal rat, and normal man) produced 

 exactly the same result ; and I must accordingly attribute 

 to the haemolysis occurring when a small quantity of blood 

 is placed in a large volume of water this phenomenon of 

 agglutination of the bacilli in watery emulsion of plague 

 culture. 



For making, therefore, a trustworthy test experiment 

 as to agglutination of the bacilli of plague by a given 

 sample of blood, neither bouillon emulsions nor watery 

 emulsion of plague culture must be used. The test should 

 always be made with a salt solution emulsion prepared 

 as described above. A good salt emulsion in a control 

 microscopic specimen sealed up shows, even after twenty- 

 four hours, the bacilli in an isolated condition. 



Next as to the blood to be tested. Comparative 

 observations which I have made in this respect show that 

 care is required to add to the emulsion the defibrinated 

 blood or blood serum, not blood in which complete 

 separation of the fibrin has not yet taken place ; because 

 in the process of coagulation apparent agglutination of 

 the bacilli through entanglement of them in fibrin threads 

 might easily be mistaken for real agglutination. 



Another point that requires elucidation is this : 

 Granted that a proper salt emulsion of plague bacilli is 



