CULTIVATION AND EXAMINATION . 33 



To reduce caramelization the sugar is added just prior to final steri- 

 lization. 



Czapek's solution agar is not offered as an optimum substratum for any- 

 particular species, but as a mixture approximately neutral in reaction, 

 which is readily made in any laboratory in fairly uniform manner, and which 

 permits moderately vigorous growth of nearly all of the saprophytic Asper- 

 gilli. The quantities of mycelium and conidia produced by many forms 

 are much greater upon other media, but for comparative study, a moderate 

 growth of the majority of the species is more useful than the great mass of 

 mycelium ard conidia which are readily obtained by using enriched sub- 

 strata. 



Since the purpose of the Czapek formula is to insure the presence of the 

 chemical elements required in quantities sufficient to support good growth, 

 it is frequently modified as to quantities and nutrients introduced. For 

 some Aspergilli such as the A. glaucus group, the addition of 20 percent or 

 even 40 percent of sucrose has proved useful. Ammonium nitrate is some- 

 times substituted for sodium nitrate but with the loss of information as to 

 whether the mold utilizes the ammonia or the nitrate, or both. Dextrose 

 is commonly substituted for sucrose. The monobasic potassium phosphate 

 prevents precipitation of certain components in sterilization, but it produces 

 an acid instead of a neutral medium, hence complicates many pieces of work. 

 The introduction of peptone or yeast extract increases the sporulation of 

 some forms. These and other changes are made, however, by investigators 

 who still refer to Czapek's solution as the basis of their work. 



Biourge, in his monograph of Penicillium (1923) and in his unpublished 

 Manuscript of Aspergillus (1939), put much emphasis upon the method of 

 preparing the neutral Raulin medium which he used for the growth of the 

 colonies analyzed in making his species diagnoses. 



Neutral Raulin's Solution — Dierckx-Biourge 



1. Magnesium carbonate 0.40 gram 



Tartaric acid 0.71 gram 



Triturate in a mortar with a few drops of distilled water and add quickly to a 

 flask of distilled water; make up to 100 ml. 



2. To a liter flask with 800 to 900 ml. distilled water add: 



Sucrose 46.60 grams 



Ammonium nitrate 2.66 grams 



Ammonium phosphate 0.40 gram 



Potassium carbonate 0.40 gram 



Ammonium sulphate 0.16 gram 



Zinc sulphate 0.04 gram 



Iron sulphate 0.04 gram 



3. Add 66 to 67 ml. of the magnesium tartrate solution (1) to the mineral salt- 

 sucrose solution (2) and make up to 1,000 ml. with distilled water. 



