790 METHODS OF INVESTIGATING BACTERIA. 



sugar; for bacteria the most suitable substrata are those 

 which contain a large amount of water, and of which the 

 reaction is neutral or alkaline. 



As nutrient soil for mould fungi we employ decoctions of 

 dried plums and other fruits ; decoctions of the fresh dung 

 of herbivorous animals; decoctions of yeast containing a 

 large amount of sugar; spread out dung of herbivorous 

 animals; pieces of bread which may be impregnated with 

 various decoctions ; a paste made of bread, &c. If the sub- 

 strata are not sufficiently acid they may be made so by 

 means of tartaric acid (2 to 5 per cent., according to the con- 

 centration of the nutrient solution) or phosphoric acid (1 to 

 1 per cent.). In the case of yeast fungi we select a decoction 

 of malt, wort, or one of the above-mentioned decoctions, to 

 which grape sugar is added ; in the case of bacteria, urine, 

 hay infusion, meat infusion, &c., to which may be added the 

 ashes of yeast, cigars, &c., and of which the reaction should 

 be as far as possible neutral, or at the most very slightly acid 

 or alkaline. 



For saprophy- Pasteur formerly recommended the following as a pure 

 tic bacteria, artificial nutrient solution: 100 parts of water, 10 parts of 

 candy sugar, 1 part of tartrate of ammonia, and the ashes 

 from 1 part of yeast, the weight of the latter being about '075 

 of that of the whole mixture. Bucholtz replaced the yeast 

 ashes in this solution by "5 grm. of phosphate of potash. 

 Cohn selected the following mixture : "1 grm. of phosphate 

 of potash, '1 grm. of crystallised sulphate of magnesia, *01 

 grm. of tribasic phosphate of lime, 20 grm. of distilled water, 

 and "2 grm. of tartrate of ammonia. These and similar 

 nutrient solutions were, however, imperfect in various ways, 

 as has recently been discovered by Niigeli. As the result of 

 numerous experiments as to the nutriment of the lower 

 fungi, Nageli recommends the following solutions as normal 

 fluids for bacteria (from these, solutions suitable for mould 

 and yeast fungi can be readily prepared by the addition of 

 sugar and acid) : 



1. Water 100 ccm., tartrate of ammonia 1 grm., biphosphate 

 of potash (K 2 HP0 4 ) '1 grm., sulphate of magnesia '02 grm., 

 and chloride of calcium "01 grin. 



Instead of the tartrate of ammonia we may employ acetate 

 or lactate of ammonia, &c., or even asparagine or leucine. 



2. Water 100 ccm., peptone or soluble albumen 1 grm., 

 biphosphate of potash (K 2 HP0 4 ) "2 grm., sulphate of 

 magnesia '04 grm., chloride of calcium '02 grm. 



3. Water 100 ccm., cane sugar 3 grm., tartrate of ammonia 

 1 grm., and mineral salts as in No. 2. 



