PLAGUE 137 



growth resembles a thistle funnel. On gelatin plates circular, granu- 

 lar, or banded colonies are formed, and these liquefy and sink into the 

 plate in two or three days. On agar containing blood, a clear haemo- 

 lyzed zone is formed round each colony. 



(2) On testing with an agglutinating serum prepared by injecting 

 known cholera vibrios into rabbits, clumping should occur at a dilu- 

 tion comparable with that in which the genuine vibrio is clumped. 

 (This reaction may also be tested on the vibrios in the stools, and a 

 rapid diagnosis made in this way.) 



(3) On peritoneal injection, it causes acute fatal peritonitis in guinea- 

 pigs. 



In general, the recognition of the cholera vibrio is not difficult, but 

 recent investigations show that marked variations occur, and that 

 organisms differing somewhat widely from the type appear to be 

 able to cause choleraic disease. This introduces very serious diffi- 

 culties, the solution of which is not clear, but in the great majority 

 of cases the organism conforms to the type given above. 



PLAGUE 



The bacteriological diagnosis of plague should be made 

 by an expert; not because it is difficult, but because so much 

 hinges upon it at least in this country. A brief account of 

 the method by which a practitioner who was unable to obtain 

 expert help might proceed may not be out of place. 



The plague bacillus is a short and rather thick rod which 

 occurs in vast numbers in the bubo, in the blood, and in the 

 internal organs. It does not stain by Gram's method, and 

 when stained by other processes it often exhibits a charac- 

 teristic polar staining, the ends of the bacillus being coloured 

 deeply, whilst the intervening portions remain colourless 

 (Plate II., Fig-. 4). It might be mistaken for a diplococcus; 

 it could not be mistaken for the pneumococcus (to which it 

 has some resemblance), as that organism stains by Gram. 

 Degenerate forms which resemble cocci, etc., often occur in 

 cultures, but are seldom met with in the body during life. 



The diagnosis may be made by an examination of fluid 

 aspirated from the bubo or of the blood. In bubonic cases 

 the former method should always be adopted, as the bacilli 

 are present therein in large numbers, and generally in pure 

 culture; the amount of fluid which has to be removed is very 

 small, even if cultures have to be taken. 



When this is not the case two films should be made in the 

 way already described, fixed and stained, the one by dilute 



