CULTIVATION AND PRESERVATION OF PENICILLIA 67 



Steep Agar 



This medium is prepared by adding to a standard Czapek's solution 1 

 percent of concentrated corn steep liquor. The pH is adjusted to 7.0 

 with normal NaOH prior to the addition of 1.5 percent agar. The me- 

 dium is sterilized in the same manner as Czapek's. 



Steep agar, as this enriched substratum is called, is particularly useful 

 in the study of Penicillia since many species make a fairly luxuriant growth 

 without losing characteristic colony patterns as on malt agar. Used 

 in conjunction with standard Czapek's agar, the medium is likewise useful 

 for revealing vitamin and other nutritional deficiencies since certain species 

 and strains that grow sparsely and atypically on Czapek show a normal 

 and luxuriant development on steep agar. In the present study we have 

 made it routine practice to incorporate into specific diagnoses supple- 

 mental notes made from this medium. 



Modifications of Czapek's solution agar involving enrichment with one 

 percent yeast extract, one percent peptone, or one percent hydrolyzed 

 casein instead of steep liquor result in media that produce colonies essen- 

 tially similar to the above in rate of growth, texture, pigmentation, and 

 spore production. 



By substituting other carbon sources for sucrose and other nitrogen 

 compounds for NaNO, , agar media suitable for the presumptive determina- 

 tion of certain nutritional deficiencies encountered in the Penicillia may be 

 readily prepared. 



Malt Extract Agar 



After many unsatisfactory experiences with brewery wort, and con- 

 fronted with increasing difficulties in obtaining it in America, Thom 

 followed Blakeslee, in his study of the Mucors, in substituting an artificial 

 wort made with dried malt-extract. For the present study we have em- 

 ployed a malt agar of a composition recommended by Blakeslee (1915) 

 as follows: 



Malt extract (Difco) 20.0 grams 



Dextrose 20.0 grams 



Peptone 1-0 gram 



Agar 25.0 grams 



Distilled water 10 liter 



The agar is melted in water in the autoclave prior to the addition of the 

 nutrients. The pH is approximately 4.7 and is not adjusted. Using 

 2.5 percent agar, the medium should set firm when sterilized in the usual 

 manner. 



Bacto wort and malt extract agars, as marketed by the Digestive Fer- 



