10 MICRO-ORGANISMS IN WATER 



from fat as possible, is finely minced and infused with 

 one litre of cold distilled water and allowed to stand 

 for twenty-four hours in a cold place (in hot weather it 

 should be placed in a refrigerator) ; the whole mass is 

 then strained through hnen, as much of the liquid being 

 pressed through as possible, distilled water being added, 

 if necessary, to restore its volume to a litre. To this 

 clarified hquid are then added 100 grms. of French 

 leaf gelatine, 10 grms. of dry peptone, and 5 grms. of 

 common salt, after which the whole is placed in the 

 steamer for about one hour until the complete solution 

 of the gelatine and peptone has taken place. The re- 

 sulting liquid, which exhibits a distinctly acid reaction, 

 must be carefully neutrahsed and rendered faintly alka- 

 line with a solution of carbonate of soda.^ The faintly 

 alkaline liquid is then clarified by mixing with it the 

 whites of two or three eggs, along with the broken 

 sheUs, the whole being again placed in the steamer for 

 from fifteen to twenty minutes. The coagulated albu- 

 men rises to the surface, and carries with it the other 

 solid particles suspended in the liquid. On then strain- 

 ing through linen a fairly clear liquid is obtained, 

 which is finaUy clarified by passing through ribbed 

 filter-paper, the filtration being most conveniently 

 carried on in the steamer, which should, however, be 

 only gently heated. The filtrate must be rejected until 

 it runs perfectly clear and limpid. The filtrate is col- 

 lected in a flask, subsequently plugged with sterile 

 cotton-wool, and on cooling sets to a straw-coloured 

 transparent jelly. Whilst still liquid it is poured into 

 test-tubes which have been previously sterilised and 

 plugged with sterile cotton-wool. The most convenient 

 quantity to take for each tube is 10 c.c, and it is best 

 to pour the gelatine from the flask into a small measur- 



^ In connection with the neutralisation of culture media see pp. 63-66. 



