NUTRIENT MEDIA AND METHODS OF CULTIVATION. 



101 



squeezing through a linen cloth or a meat press. The red juice thus 

 obtained must be brought up to a litre by transferring it to a large 

 measuring glass and adding distilled water. It is then poured 

 into a sufficiently large and strong beaker, and set aside after the 

 addition of 10 grammes of peptone, 5 grammes of common salt and 

 100 grammes of best gelatine. 



In about half an hour the gelatine is sufficiently softened, and 

 subsequent heating in a water-bath causes it to be completely 



FIG. 30. HOT Am STERILISKK. 



dissolved. The danger of breaking the beaker may be avoided by 

 placing a cloth, several times folded, at the bottom of the water-bath. 



The next process requires the greatest care and attention. Some 

 micro-organisms grow best in a slightly acid, others in a neutral 

 or slightly alkaline, medium. For example, for the growth and 

 characteristic appearances of the comma bacillus of Asiatic cholera 

 a faintly alkaline soil is absolutely essential. This slightly alkaline 

 medium will be found to answer best for most micro-organisms, and 

 may be obtained as follows : 



With a clean glass rod dipped in the mixture, the reaction 

 upon litmus- paper may be ascertained, and a concentrated solution 

 of carbonate of soda must be added drop by drop, until red litmus- 



