402 



PLAGUE 



Thus, in the tea-plantations at Catchar,in 6,549 persons who were 

 not vaccinated, there were 198 cases, with 124 deaths, whilst in 

 5,778 vaccinated, there were 27 cases, with 14 deaths i.e., the 

 incidence fell from 3 to under 0-5 per cent., the case-mortality 

 being 62 and 51 per cent, respectively. Numerous other 

 examples might be quoted, and the value of the method is now 

 proved to the full. 



Plague. 



The plague bacillus produces a powerful endotoxin, cultures 

 killed by heat being markedly irritating. There is some evidence 

 that a true exotoxin may be produced, though in small amounts. 

 Filtrates from young cultures are devoid of toxicity, whereas 

 those from older ones may be fairly potent. The fluid portion 

 of culture (in broth grown at 20 C. and kept well aerated) 

 two months old was found by Markl to kill rats in doses of 

 c'i c.c. This might, of course, be due to an autolysis of the bacilli, 

 but this seems improbable from the fact that the toxicity of the 

 nitrate is very easily destroyed by heat, whereas the endotoxin is 

 thermostable. These filtrates have slight immunizing properties, 

 but the plague anti-endotoxin has not been closely studied. 



Immunity appears to be due to the production of bacteriolytic 

 substances : antiplague serum, prepared by immunizing horses 

 first with dead and then with living bacilli, is powerfully bacteri- 

 cidal. According to Wright, the plague bacillus is quite insensible 

 to the bactericidal action of human blood, and recovery is due to 

 opsonization followed by phagocytosis. 



The agglutination reaction is well marked in artificially 

 prepared immune serum, which may clump at i : 1,000 or more 

 and may be of use in the identification of a doubtful bacillus. It 

 s not usually marked, and may be absent in human cases of the 

 disease, and the diagnosis is most frequently made by the 

 identification of the bacillus in fluid from a lesion or from the 

 blood or sputum. According to Cairns, the blood does not usually 

 clump until the disease has been in progress for about a week. 

 The strength of the reaction is not great, rarely rising above i : 50, 

 and is sometimes as low as 1:3 or 1:5. The macroscopic 

 method is advisable. 



The curative treatment of the disease by specific methods 

 resolves itself into the use of a serum, vaccines not having been 

 tried, as far as I am aware. Several sera are prepared, but not all 



