NUTRIENT MEDIA AND METHODS OF CULTIVATION. 



101 



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

 ohtained nmst be brought up to a litre by transferring it to a large 

 measuring glass and adding distilled water. It is then poured 

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

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

 11)0 grammes of best gelatine. 



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

 subsequent heating iu a water-bath cairses it to ba completely 



Fig. 30. — Hot Am Stekiliser. 



dissoh'ed. 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 sUghtly acid, others in a neutral 

 or slightly alkaline, medium. For example, foi- 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- 



