THE CHEMICAL COMPOSITION OF BACTERIA 11 



m plant and animal tissues, for example, albumins, globulins, 

 and phosphorised substances such as nucleins and nucleinic 

 acid. There is also evidence that in the bacteria, as in the 

 higher- cells, lipoidal bodies are intimately associated with the 

 proteid elements. Further, various mineral salts, especially 

 those of sodium, potassium, and magnesium, are constituents of 

 bacterial protoplasm. All the constituents show great varia- 

 tions, dependent not only on the species under investigation, 

 but also on the composition of the culture media, on the 

 temperature of growth, and on the age of the culture. 



Many species of bacteria, when growing in masses, are 

 brilliantly coloured, though few bacteria associated with the 

 production of disease give rise to pigments. In some of the 

 organisms classed as bacteria a pigment named bacterio-purpurin 

 has been observed in the protoplasm, and similar intracellular 

 pigments probably occur in some of the larger forms of the 

 lower bacteria and may occur in the smaller ; but it is usually 

 impossible to determine whether the pigment occurs inside or 

 outside the protoplasm. In many cases, for the free production 

 of pigment abundant oxygen supply is necessary ; but sometimes, 

 as in the case of spirillum rubrum, the pigment is best formed 

 in the absence of oxygen. Sometimes the faculty of forming it 

 may be lost by an organism for a time, if not permanently, by 

 the conditions of its growth being altered. 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, namely, the lipochromes. These lipochromes, which get their 

 name from the colouring matter of animal fat, include the colouring 

 matter in the petals of Ranunculacese, 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. 



The Classification of Bacteria.— In what we have to say 

 under this heading we shall chiefly confine ourselves to the 

 characters of the pathogenic bacteria. There have been 

 numerous schemes set forth for the classification of bacteria, the 



