BACTERIOLOGICAL ANALYSIS. 653 



Of the remaining tests, the indol reaction should be tested by 

 the benzaldehyde method, seven days being the most useful time 

 in most cases. 



There is no need to dilate on the value of the agglutination 

 reaction in certain cases where a stock standard immune serum 

 can be used to test a culture, or of immunity experiments on 

 animals, seen best in the usual critical test for a suspected diph- 

 theria culture. 



Vosges and Proskauer's reaction is seldom used, and is mani- 

 fested by a red colour on the addition of potash to a glucose broth 

 culture of certain organisms. 



The test for nitrites and nitrates need not be further referred 

 to ; they have as yet found slight application in this method, 

 though it is likely further experience will show them to be useful 

 in certain cases. 



The cholera red reaction is merely the test for indol and 

 nitrites, and is performed by the addition of sulphuric acid to a 

 culture which, if it contains both indol and nitrites, will give a red 

 colouration. 



The Biochemical Method and the Colon Bacilli. — The bio- 

 chemical method is especially useful in certain branches of bac- 

 teriology. It is the only way, for instance, of separating the vast 

 army of colon bacilli, by which term I include all non-gelatine 

 liquefying in seven days. Gram-negative bacilli, which grow well 

 on agar at 37° C in 20 hours, do not peptonise milk. Tnis group 

 includes such widely divergent types as B. lactis cerogenes (Emmerich) , 

 B. coli communis {'Eschexich), B. pneumonice (Friedlander), B. acidi 

 lactici (Hueppe), B. enteritidis (Gaertner), B. paratyphosus, A and 

 B (Schottmuller), B. suipestifer (Salmon), B. enteritidis (Morgan), 

 B. hog cholera (McFadyean), B. typhosus (Eberth Gaffky), B. 

 dysentericB (Flexner), B. dysenterice (Shiga), and a vast number of 

 other types. It will be simplest if I demonstrate the biochemical 

 method first of all on these organisms, for it is here universally 

 admitted to be most useful. 



By referring to Table I (general classification of the colon 

 organisms) it will be seen that the first step after assuring ourselves 

 of the morphology, staining reactions, and absence of liquefying 

 action on gelatine of the bacillus, is to find if it is a gas-former or 

 not. Straight away it may be said that the vast majority of the 

 colon bacilli are gas-formers, and by some the term colon bacilli 

 is restricted to these. I think it is a mistake to thus restrict the 

 name colon bacilli, preferring to apply this to all the organisms as 

 above described. The name aerogenes is a better term to apply 

 to those which form gas as weU as acid, and anaerogenes to those 

 which do not form gas. Tubes of glucose litmus peptone water 

 in which are gas-collecting Durham's tubes are the means of 

 testing this property (no organism yet isolated belonging to the 

 colon group failing to give gas on glucose, gives gas on any other 

 sugar). 



