THE CLASSIFICATION OF BACTERIA. n 



Thus, for example, if the B. pyocyaneus be exposed to the 

 temperature of 42 C. for a certain time, it loses its power of 

 producing its bluish pigment. Pigments formed by bacteria 

 often diffuse out into, and colour, the medium for a considerable 

 distance around. 



Comparatively little is known of the nature of bacterial pigments. Zopf, 

 however, has found that many of them belong to a group of colouring matters 

 which occur widely in the vegetable and animal kingdoms, viz., the lipo- 

 chromes. These lipochromes, which get their name from the colouring 

 matter of animal fat, include the colouring matter in the petals of Ranun- 

 culaceae, the yellow pigments of serum and of the yolks of eggs, and many 

 bacterial pigments. The lipochromes are characterised by their solubility in 

 chloroform, alcohol, ether, and petroleum, and by their giving indigo-blue 

 crystals with strong sulphuric acid, and a green colour with iodine dissolved 

 in potassium iodide. Though crystalline compounds of these have been 

 obtained, their chemical constitution is entirely unknown, and even their 

 percentage composition 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 

 Ruppel, appear to have been allied to peptone, and which cer- 

 tainly differed from nucleo-proteids in not containing phos- 

 phorus, but many of the proceids 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, potas- 

 sium, and magnesium. The amount of different constituents 

 varies according to the age of the culture and the medium used 

 for growth, and certainly great variation takes place in the 

 composition of different species. 



The Classification of Bacteria. There have been numerous 

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

 mental principle running through all of which has been the 

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



