II.] PREPARATION OF CULTURE MATERIAL. 17 



cultivations be practically, lost. But if this last cultivation 

 should be found to act in the same manner pathogenically, 

 i.e. if every droplet of it, charged with the new brood of the 

 organism, nevertheless possesses full pathogenic power, then 

 it is logical to say that this pathogenic property rests with 

 the organism. For this and other reasons it is of essential 

 importance to be able to carry on successive cultivations 

 of one and the same organism without any accidental con- 

 tamination or admixture, /.<?. it is necessary to carry on pure 

 cultivations. 



ARTIFICIAL CULTIVATION MEDIA. 



A. FLUIDS. 



As fluid nourishing material the following are used with 

 preference : 



i. Broth made from Meat pork, beef, rabbit, chicken. The 

 connective tissue and fat are first cut out from the fresh meat 

 in the case of rabbit or chicken the whole animal without 

 head or viscera is used and then placed in water and boiled. 

 Generally for each pound half an hour's good boiling is 

 allowed. With regard to the quantity of water, each pound 

 of meat ought to yield ultimately at least one pint of broth. 

 When boiled, the broth is allowed to stand, the fat is skimmed 

 off, and the broth well neutralised, or even made faintly 

 alkaline by adding liquor potassae, or, better still, carbonate 

 of sodium. 



The fresher the meat the less acid (sarcolactic acid) is in 

 the broth before neutralisation. The broth is then filtered 

 through a filter, previously overheated (see below), into flasks 

 previously sterilised (see below). As a rule beef broth is 



c 



