652 PROCEEDINGS OF SECTION I. 



is only when we find out what it does, watch the free-swimming 

 vertebrate become attached and vegetate, that we reahse its place 

 in nature. How much of the appearance of the bacterium is not 

 the top hat and frock coat of plenty or the dungaree of adverse 

 circumstances. But I imagine someone thinking of the contrast 

 between himself and the slant-eyed Chinaman. Here is morpho- 

 logy vindicated ! But granting, as we must, that appearances in 

 some cases are useful enough, could not anyone of us with his 

 eyes shut tell the Chinaman by what he does ? Admittedly the 

 most certain way will be to use both methods. 



The biochemical method attempts, by the inquiry into the 

 chemical, physical and biological properties of organisms, to help 

 in the separation into types or units. In this laboratory the general 

 method is as follows : — 



After having noted the usual morphological and staining 

 properties, the organism is grown generally for a week on — 



1. Gelatin : To test for liquefaction. 



2. Litmus Milk : To note peptonisation or acid production 



or clotting. 



3. Various Carbohydrates : To note formation of acid, or 



acid and gas, or no action. 



4. Peptone Water : To test for indol. 



According to circumstances fuller tests are added if they are 

 useful — e.g., agglutination reactions, immunity experiments, Vosges 

 and Proskauer's reaction, and test for nitrates or nitrites. 



Technique. — There is little to be said on this account. Gelatine 

 is inoculated in the usual way and kept under observation for 

 varying periods, depending on the type of organism in question. 

 With colon bacilli the test should last a week for general purposes, 

 but for more complete separating a month is necessary, as some 

 colon bacilli, though roughly speaking not gelatine liquifers, are 

 able to do so after a long while [B. cloacce, B. coscoroba). The 

 inoculation of litmus milk needs no comment, but it should be 

 stated that though for general purposes a few days' observation is 

 sufficient, in some cases 15 days are necessary. The observer notes 

 acidity, alkalinity, decolorisation, peptonisation, or clotting, or 

 any combination of these. 



The carbohydrate tests form the principal part — the very 

 backbone, so to speak, of the biochemical method. They are put 

 up in solution or suspension in litmus-peptone water, and in each 

 tube is a little inverted tube (Durham's) to catch any gas formed. 

 The points noted are acid formation, or acid and gas formation. 

 The carbohydrates, familiarly known as sugars, most frequently 

 used can be seen by reference to tables. The most important 

 are what we know at the laboratory as " the first five sugars " — 

 glucose, mannit, dulcit, lactose, and cane sugar ; while for special 

 cases adonit, inosit, sorbit, and raffinose are of prime importance. 

 This will be referred to further later on. 



