BACTERIOLOGICAL ANALYSIS. 651 



But having arrived this far we are met by difficulties, inas- 

 much as there are bridging forms between all three main groups, 

 and an organism may frequently grow as a coccus one time and 

 later on as a bacillus. Also, if we accept the three groups as being 

 on the whole constant, yet each group contains a vast number of 

 classes and types indistinguishable from each other. A few types 

 can be more or less weeded out by considerations of size, shape, 

 presence and, if present, position and shape of spores, presence, and, 

 if present, number and situation of ffagella, arrangement of indi- 

 vidual elements to each other ; but this is all. 



The reactions to various methods of staining have proved of great 

 value, and Gram's method holds the place of honour, enabling us 

 to classify all bacteria into two classes — those which do and those 

 which do not stain by Gram. This reaction has enabled us to 

 sharply separate a number of types similar in other ways, and 

 being most likely the indication of a physiological peculiarity of the 

 organism, probably leads towards a natural classification. Zeill 

 Neillsen's method, originally used for the tubercle bacillus, enables 

 us not only to demonstrate bacilli which other stains fail to show, 

 but again gives us another means of classifying into two groups. 

 Other staining methods — Neisser's, Loefifler's, and a number of 

 less important ones — have enabled us to get a much greater insight 

 into the characteristics of different bacteria, and so to separate and 

 classify. 



Cultural Methods. — It is to the method of culture that bacteri- 

 ologists probably owe most. Unfortunately, cultures are not 

 available in all cases, and numerous bacteria grow identically, 

 though quite obviously of different type ; still, by the study of 

 the nature of growth, rate of growth on different media, much has 

 been done, and for other practical purposes cultures are of utmost 

 importance ; and, lastly, the method of culture is the direct pro- 

 genitor of the biochemical method. 



The Biochemical Method. — I take it that the biochemical 

 method attempts to find out what a bacterium does in contra- 

 distinction to what it looks like, each way of investigation of course 

 leading up to the question, what a bacterium is in relation to other 

 bacteria. This aspect of inquiry has been criticised. It has been 

 said that it is fallacious to attempt to classify by the action of an 

 organism, and has been likened to attempting to classify individual 

 men not on appearance, etc., but by their actions. I cannot help 

 thinking that this was a bad analogy, for we most assuredly do 

 get a more useful idea of a person if we know what he does. It is 

 usual to classify people by their features, shape, or size, but I am 

 sure if we could find out everything that each of us is capable of 

 doing we should be nearer truth in our classification than by any 

 method depending on length of moustache, shape of head, etc. 



How much of what we see in nature outside of the bacteria 

 altogether is fallacious. In the cunjevoi, familiar member of 

 ascidia adhering to the wharf, it is hard to see the vertebrate ; it 



