414 THE HEMORRHAGIC SEPTICEMIA GROUP 



Active immunization of man against plague has been accomplished 

 by Haffkine, using broth cultures of plague bacilli grown in shallow 

 layers of broth containing droplets of cocoanut or other neutral oil 

 on the surface to increase the development of the organisms by stalac- 

 tite formation; after about six weeks' incubation, during which time 

 several crops of bacilli develop and sink to the bottom, the culture 

 is heated to 60 to 65 C. for an hour, and 0.5 per cent, phenol is 

 added. 2 to 3.5 c.c. of the killed culture are injected subcutaneously 

 into adults, proportionately smaller amounts into children. Usually 

 a second injection is given, somewhat larger in amount, after ten 

 days. The German Plague Commission 1 used forty-eight-hour agar 

 cultures of virulent plague bacilli emulsified in salt solution and 

 sterilized at 65 C.; 0.5 per cent, phenol was added as a preservative. 

 The amount for injection into an adult was the equivalent of one 

 agar culture of the organism. Available evidence indicates that 

 prophylactic inoculation against plague reduces materially both the 

 morbidity and mortality of the disease. The protection, as the 

 statistics show, is by no means absolute, and ' it appears that the 

 duration of resistance to infection is indeterminate, probably on the 

 average several months. A serum obtained from horses immunized 

 against plague bacilli has been prepared, but its use in man has on 

 the whole been irregular and disappointing; the chief practical use 

 appears to be in those cases where exposure to infection is reason- 

 ably certain, as for example, in those attending plague patients. The 

 excessive cost of the serum is prohibitive for general use. 



Transmission and Plague. The Interim Report of the Advisory 

 Committee for Plague Prevention in India 2 contains a very excellent 

 summary of the mechanism of plague transmission by the flea. In 

 bubonic plague, the most common type seen in man, the plague bacilli 

 are locked up in the body, as it were, and can not of themselves escape 

 to other hosts. The rat is usually the source of infection in plague 

 epidemics, and rat fleas, Xenopsyllus cheopis, transmit the disease 

 from rat to rat and from rat to man. When the host dies (rat or man) 

 its ectoparasites escape if possible to living hosts. It was shown by 

 the Indian Commission 3 that fleas from plague-infected rats frequently 

 contained large numbers of plague bacilli in their intestinal tracts, 



1 Gaffky, Pfeiffer, Sticker, and Dieudonne, Bericht u. d. Thatigkeit dcr zur Erfor- 

 schung der Pest im Jahre 1897, etc., Berlin, 1899. 



2 Jour. Hyg., 1910, x, No. 3. 



3 See Jour. Hyg., 1906, 1907, 1908, 1910, for a most complete discussion of the relation 

 of fleas to the transmission of plague. 



