n] PREPARATION OF CULTURE MATERIAL 29 



perature of 32" to 38° C., and then boiled on the next day 

 for half an hour in the usual way. The supposition is 

 made, that if by any chance after twice boiling the broth it 

 should contain unchanged spores of bacilli — the only 

 organisms that will resist boiling, although they do not resist 

 boiling for more than several minutes — the spores would 

 germinate into bacilli when kept for twenty-four hours in 

 the' incubator at 32° to 38°, and these would then be killed 

 by the third boiling. As a matter of fact I have not as a 

 rule found any contaminating germs survive the second 

 boiling. It is of course to be borne in mind that during 

 the first as well as second and subsequent boiling the cotton- 

 wool plug is not removed from the mouth of the flask, but 

 is only raised out half its length from the neck. The 

 cotton wool and the cotton-wool cap and beaker are re- 

 placed immediately or simultaneously with the turning off' 

 of the burner. 



2. Peptone and Salt Solution. — Beef peptone (Savory and 

 Moore's) is dissolved in distilled water, over a burner, to 

 the amount of i per cent. ; to the solution is added common 

 salt to the amount of o"5 per cent. ; so that every 100 ccm. 

 of the fluid contains one gramme of peptone and \ gramme 

 of salt. When dissolved it is made faintly alkaline, and 

 then filtered (the vessels being of course also in this, as in 

 all other cases, sterilised by heat). 



A 10 per cent, peptone, 5 per cent, salt solution, repre- 

 sents a useful stock, because it can be kept as a smaller bulk, 

 and used by dilution if large quantities of i per cent, peptone 

 be required. 



For general use where broth is required as culture fluid, 

 the above stock-broth, plus i per cent, peptone and 0-5 per 

 cent, salt, represents an excellent fluid, the nutrient broth : it 

 is of course made faintly alkaline after the peptone is added 



