THE CLASSIFICATION OF BACTERIA 11 



petroleum, and by their giving indigo-blue crystals with strong sulphuric 

 arid, and a green colour with iodine dissolved in potassium iodide. 

 Though cry stal line compounds of these have been obtained, their 

 cht inical constitution is entirely unknown, and even their percentage 

 i (imposition is disputed. 



Some observations have been made on the chemical structure 

 of bacterial protoplasm. Nencki isolated from the bodies of 

 certain putrefactive bacteria proteid bodies which, according to 

 Kuppel, appear to have been allied to peptone, and which 

 differed from nucleo-proteids in not containing phosphorus, 

 but many of the proteids isolated by other chemists have 

 been allied in their nature to the protoplasm of the nuclei 

 of cells. Buchner in certain researches obtained bodies of this 

 nature allied to the vegetable caseins, and he adduces evidence 

 to show that it is to these that the characteristic staining 

 properties are due. Various observers have isolated similar 

 phosphorus-containing proteids from different bacteria. Besides 

 proteids, however, substances of a different nature have been 

 isolated. Thus cellulose, fatty material, chitin, wax-like bodies, 

 and other substances have been observed. There are also found 

 various mineral salts, especially those of sodium, potassium, and 

 magnesium. The amount of different constituents varies ac- 

 cording to the age of the culture and the medium used for 

 m<>\\tli, and certainly great variation takes place in the com- 

 position of different species. 



The Classification of Bacteria. There have been numerous 

 schemes set forth for the classification of bacteria, the fuixla- 

 nii'iital principle running through all of which has been the 

 recognition of the two sub-groups and the type forms mentioned 

 in the opening paragraph above. In the attempts to still 

 furl her subdivide the group, scarcely two systematists are agreed 

 a- to the characters on which sub-classes are to be based. Our 

 (resent knowledge of the essential morphology and relations of 

 bacteria is as yet too limited for a really natural classification 

 to be attempted. To prepare for the elaboration of the latter, 

 Marshall Ward suggested that in every species there should be 

 studied the habitat, best food supply, condition as to gaseous 

 environment, range of growth temperature, morphology, life 

 hUtoiy. >pecial properties, and pathogen icity. Some recent 

 at! i 'in j.ts to carry out such a plan will be referred to in 

 -onnectioii with the principles of general bacteriological 

 diagnosis (p. 135). 



\\V must thus be, content with a provisional and incomplete 

 We have said that the division into lower and 



