NUTRIENT MEDIA. 33 



artificial nutrient media, either readily (example, Bacte- 

 rium typhi) or with more difficulty (example, Microcpc- 

 cus gonorrhoeas). Of the inhabitants of the inanimate 

 surroundings of man, i. e., the so-called saprophytes, 

 most are easily cultivated on artificial media, similar to 

 those employed for parasites, while others as, for exam- 

 ple, saliva bacteria and certain water bacteria offer great 

 or in part insurmountable difficulties in their cultivation. 



All nutrient media for bacteria must be rich in water ; 

 the presence of salts, and sources for the supply of carbon 

 and nitrogen are indispensable. Most varieties of prac- 

 tical importance and all pathogenic varieties prefer a 

 medium containing albumin which is faintly alkaline in 

 reaction. 



In some cases the demands of the bacteria as regards 

 the composition of the nutrient medium are very different. 

 As shown by Mead Bolton, a number of water bacteria 

 (Bacillus aquatilis Fliigge and B. erythrosporus Fliigge) 

 are contented with water which has been twice sterilized 

 in glass vessels (Z. H. i, 76). Here an increase of the 

 bacteria must occur at the cost of traces of impurities, or 

 of the ammonia and C0 2 of the atmosphere. 



Almost simultaneously Heraeus (Z. H. i, 193) observed 

 a variety of bacterium, which thrived in water which con- 

 tained ammonium carbonate as the only source of carbon 

 and nitrogen, being free from every organic nutrient ma- 

 terial. Here, then, there occurred the elaboration of 

 living substance from simple materials, just as occurs 

 in the higher plants which work with chlorophyll aided by 

 sunlight. Hiippe and Winogradsky have demonstrated 

 by extensive studies the truth and importance of this ob- 

 servation. It appears that the energy necessary for the 

 synthesis of albumin is obtained by oxidation of ammonia 

 into nitric acid. Among the practically important bac- 

 teria, such unparticular ones are very few. Many allow 

 albumin to be absent from the medium and are content 

 with very simply composed nutrient solutions. Cultures 

 upon such fluids were formerly much employed, and more 

 recently Uschinsky has again experimented with simple 

 nutrient solutions. The solution of Uschinsky is as fol- 

 lows : 

 3 



