CULTIVATION AND EXAMINATION 35 



Malt Extract Agar (Blakeslee's Formula, 1915) 



Distilled water 1 ,000 cc. 



Malt extract 20 grams 



Peptone 1 gram 



Dextrose 20 grams 



Agar 20 grams 



Add dextrose just prior to final sterilization. Conidial structures are 

 generally more numerous and are often borne on shorter conidiophores, and 

 there is an almost complete absence of coloration in the substratum. Ex- 

 cept in a few isolated cases, coloration of the spore heads themselves is not 

 materially altered. While the production of exudate in the form of drops 

 is not characteristic of many of the Aspergilli, it can be generally said that 

 droplet formation on malt agar is much less than upon Czapek's solution 

 agar. 



Hay infusion agar is very useful in the isolation of Aspergilli from nature. 

 A 1 : 10 suspension of soil in sterile water is streaked on hay infusion agar 

 plates and incubated for one week to 10 days. Isolations are then made 

 from individual fruiting structures with the aid of a low-power binocular. 



Hay Infusion Agar 



Distilled water 1,000 cc. 



Decomposing hay 50 grams 



Autoclave for 30 minutes at 15 pounds. Filter. 



Infusion nitrate 1 , 000 cc . 



K 2 HP0 4 2 grams 



Agar 15 grams 



Adjust pH to 6.2± 



No Aspergillus makes a luxuriant growth upon this medium, but a great 

 variety of forms make a limited development. Furthermore, such fruiting 

 structures as are produced are generally characteristic of the different 

 species present. It thus constitutes a very favorable substratum with 

 which to analyze and isolate the Aspergilli occurring in soils or other natural 

 substrates. The medium is likewise useful for securing limited sporulation 

 of certain forms, such as Aspergillus sparsus, which fruit very sparsely upon 

 Czapek's solution agar. 



Czapek's solution agar enriched with peptone or corn steeping liquor is 

 often very useful. For example, in the cultivation of members of the 

 glaucus group, the addition of a limited amount of peptone greatly increases 

 the production of conidia, while addition of a small amount of corn steeping 

 liquor (e.g., 0.2 percent) increases the growth of most forms without mark- 

 edly affecting the character of the resulting colonies. 



