REPRODUCIBLE MEDIA 53 



the addition of agar. A medium widely used by plant pathologists 

 is potato-glucose agar: 



Peeled sliced potatoes 300 grams 



Glucose 10 grams 



Agar 15 grams 



Water 1 liter 



The medium is boiled for 20 minutes and strained through cotton. 

 The reaction, slightly acid, is not adjusted. 



Corn meal agar is also widely used. It is especially valuable in 

 observing the development of chlamydospores and for demonstra- 

 tion of mycelium in Candida albicans. Light-colored corn meal is 

 preferable. If one uses dehydrated media he should make certain 

 that no glucose has been used in the formula. 



Corn (maize) meal 40 grams 



Water 1 liter 



This is heated to 60° C. for 1 hour and stirred frequently. It is 

 filtered through paper and made up to 1 liter; then 20 grams of agar 

 is added. The reaction is not adjusted. If it is sterilized by the 

 fractional method, as is sometimes recommended, trouble may be 

 expected from resistant spores of bacteria in this non-acid medium. 



Brewery bacteriologists use beer wort and wort agar for the culti- 

 vation of their yeasts, and winery bacteriologists use grape juice or 

 must. Industrial yeasts are said to maintain their special fermenta- 

 tion characteristics better on these natural substrates than on more 

 artificial media. Malt-extract agar may be substituted for beer wort. 

 These media naturally have reactions about pH 4.5 and, if auto- 

 claved, the agar may be softened. Diluted honey has been used for 

 growing both yeast and molds, but it is variable in composition and, 

 save for the special study of honey and nectar yeasts, not very useful. 



Manure infusion agar has been widely used for the cultivation of 

 various coprophilic fungi. The following method is presented by 

 Gwynne-Vaughan and Barnes.^"^ About 1000 grams of horse, cow, 

 or rabbit dung is soaked in cold water for 3 days ; the liquid is poured 

 off and diluted until it has the color of straw; 2.5 grams of agar is 

 added for every 100 ml. of the diluted fluid. 



Sterilized soil has been used successfully by Greene and Fred ^^ for 

 maintaining cultures of certain molds with a minimum of physio- 

 logical or morphological degeneration. 



Reproducible Media. The standard medium used by medical my- 

 cologists for the cultivation of pathogenic fungi is Sabouraud's agar. 

 As originally described, this consisted of 4 per cent of the crude mal- 



