40 PRINCIPLES OF BACTERIOLOGY 



Nuclein is found frequently. The nuclein bases xanthin, guanin, and 

 adenin have been obtained in considerable amounts. There is a 

 group of bacteria which contain sulphur viz., the beggiatoa and an- 

 other group, the cladothrix, is capable of separating ferric oxide from 

 water containing iron. 



Some light has been thrown upon the chemical composition of bacteria, 

 quantitatively, by the studies of Cramer, though so far only a few species 

 have been thoroughly investigated. The percentage of water contained 

 in bacteria grown on solid culture media, as well as the amount of ash, 

 depends largely on the composition of the media. Thus the bacillus 

 prodigiosus when grown on potato contains 21.5 per cent, of dry residue 

 and 2.7 per cent, of ash; when cultivated on turnips it contains 12.6 per 

 cent, of dry residue and 1.3 per cent, of ash. Besides the concentration 

 of the culture, its temperature and age also influence the amount of 

 residue and ash produced. The residue varies, moreover, in its com- 

 position in the same species under the influence of the culture media 

 employed. 



It appears that an additional quantity of peptone in the culture media 

 tends to increase the percentage of nitrogenous matter in the bacillus, 

 while the addition of glucose decreases it. 



Chemical Substances Necessary for the Nutrition of Bacteria. The 

 majority of bacteria are easily cultivated, but there are some for 

 which, with our present knowledge, we are unable to produce conditions 

 suited for their growth. 



All bacterial culture media must contain an abundance of water; 

 salts are also indispensable, and there must be organic material as a 

 source of carbon and nitrogen. The greater number of important bac- 

 teria and all the pathogenic species thrive best in media containing 

 albuminoid substances and of a slightly alkaline reaction to litmus. 

 The demands of bacteria in the composition of the culture media vary 

 considerably. There are some species of water bacteria, for instance, 

 which require so little organic material that they will grow in water that 

 has been twice distilled. A certain species will grow abundantly in 

 water containing ammonium carbonate in solution and no other source 

 of carbon and nitrogen. This shows the power of some bacteria of pro- 

 ducing cell substance from the simplest materials a power which 

 belongs to the higher plants which obtain their nourishment from the 

 air through their chlorophyll and the assistance of sunlight. Few bac- 

 teria, however, of any importance in medicine are so easily satisfied, 

 though there are many species which are able to develop without the 

 presence of albumin and in comparatively simple culture media, such 

 as the culture liquid proposed by Uschinsky, or the simpler one of Voges 

 and Fraenkel, which consists of water, 1000; sodium chloride, 5; 

 neutral sodium phosphate, 2; ammonium acetate, 6; and asparagin, 4. 

 In these media many bacteria grow well. 



When we consider in detail the source of the more important chemical 

 ingredients of bacteria we find that their nitrogen is most readily obtained 

 from diffusible albuminoid material arid less easily from ammonium 



