24 CULTURE METHODS AND TECHNIQUE 



has been my practice to require 50 grams dry weight of the plant 

 product. Accordingly, from a mean of several analyses brought 

 together, it would require about 490 grams of beet root, 400 grams 

 of bean stems or of string beans, 1 20 grams of dried prunes, and 

 about 390 grams of the fresh potato. 



The plant product is washed, and, if desirable, pared, cut up 

 finely, or thinly sliced, and then the necessary water is added. It 

 is next boiled in the steam sterilizer for about two hours, or in the 

 autoclave at 1 1 5 C. for twenty minutes. If necessary to boil over a 

 steam bath, a flask plugged loosely with cotton, or a small-mouthed 

 agate pitcher covered with flannel, should contain the material, so 

 that a minimum of evaporation will occur. The clear liquid is filtered 

 off through several thicknesses of filter paper into a sterile flask, 

 when it may be immediately used in making solid media, or ster- 

 ilized as usual for preservation. Where it is particularly desired 

 to obtain the clearest decoction possible, the liquid may be cooled 

 to about 60 C. under the tap, or by pouring from one vessel to 

 another, and then the white of an egg may be added. The decoc- 

 tion is again boiled for an hour in the sterilizer, or about fifteen 

 minutes in the autoclave ; and the clear liquid finally filtered away 

 from the coagulated albumen and sediment. 



It will often be necessary, or well, to make decoctions of various 

 other plants, particularly of fleshy fungi, of the host plants upon 

 which certain fungi grow, etc. Such decoctions may be particularly 

 desirable in physiological work. 



Manure decoctions of any kind are particularly serviceable in the 

 study of many saprophytic organisms, but in pathological work 

 these liquids are no more valuable than any of the plant decoctions. 

 Special emphasis might be laid upon prune juice, or prune decoc- 

 tion, especially when the fungus is one which may inhabit saccha- 

 rine fruits, berries, etc. 



It will be readily suggested to the student that plant products 

 of various kinds may be roughly grouped into such as are rich in 

 albumens, starches, sugars, etc., and these products will be selected 

 and employed in accordance with such indications with respect to 

 the needs of the fungus as are available. 



Bouillon, the chief fluid medium used for the bacteria, is an 

 extract of beef, practically a beef tea, to which peptone is added. 



