LAKOKATORY AND TEACHING METHODS 



599 



Prune Juice. 



1. Take a dozen or two of prunes and boil them in water until the water is decid- 

 edly colored with the prunc.extract. 



2. Add this prune juice to test-tubes and plug. 



3. Sterilize on three consecutive days. 



Coconut Water. — This is removed directly from the nut to sterile test-tubes by 

 means of sterile pipettes, which are useful in many ways. The pipettes should be 

 dry-heated and kept from contamination, or in long, narrow, covered tin boxes. 



Wheat Broth (After Eyre and Gasperini). 



1. Weigh out and mix wheat flour, 150 grams; magnesium sulphate, 0.5 gram; 

 potassium nitrate, i gram; glucose, s grams. 



2. Dissolve the mixture in 1000 c.c. of water heated to ioo"'C. 



3. Filter through filter paper. 



4. Fill test-tubes and sterilize on three consecutive days. 



Plant Decoctions, or Infusions in General (After Heald). — Liquid media contain- 

 ing the soluble nutrients derived from various plant structures are of special value 

 in dealing with fungi and may be used with bacteria, although they are not so 

 important for these organisms. By the selection of parts of a host plant for making 

 a medium for the growth of the attacking fungus, it will be provided with food nearer 

 to its immediate needs than from the standard nutrient media. Plant decoctions 

 may be used as liquid media, or they may serve in combination with other media 

 solidified by gelatin, or agar. 



Some of the most valuable plant decoctions are obtained from fruits, seeds, root 

 parts and other plant organs. Decoctions may be made from fresh plant parts as 

 sweet potatoes, beets, turnips, carrots, celery, bean pods, plums, apples, etc., or 

 dried plants such as dried apples, dates, beans, leaves, etc. 



In preparing either decoctions, or infusions, it is well to have the parts employed 

 in a finely divided state. The parts may be run through a food chopper or ground 

 finely by a small coffee mUl. The pharmaceutic standard should be selected for 

 decoctions and infusions, i.e. 1000 c.c. should contain the soluble constituents of 

 SO grams of dry weight of the product employed. To secure uniformity of compo- 

 sition' the following table can be used in determining the weight of the fresh product 

 to be employed. 



Table to Determine Amount of Dry Substance to be Used 



Name of plant organ 



Water 

 content, 

 per cent. 



Potato 75 



Sugar beet 82 



Carrot 87 



Celery 84 



Leaves (young , 75 



Leaves (mature) 55 



Bark (fresh) 15 



Bark (air dry) , 7 



Dry Approximate weight 



substance, yielding 50 grams of 

 per cent, dry substance, grams 



I 



45 

 85 

 93 



60 

 55 



