Chapter IV 



CULTIVATION AND PRESERVATION 

 OF PENICILLIA 



A few species of Penicillium, such as Penicillium roqueforti Thorn, P. 

 camemberti Thorn, P. expansum Link, P. italicum Wehmer, and P. digi- 

 tatimi Sacc, are so closely associated with particular products or processes 

 that the presence of a Penicillium in such situations warrants presumption 

 of identities which are usually confirmed by microscopic examination. 

 The majority of the Penicillia, however, have not been shown to bear any 

 specific relation to particular processes or products. Such organisms 

 appear as part of the complex population of stale or decaying organic 

 matter. Almost any species of Penicillium can be isolated from soil, and 

 certain species are usually present in considerable abundance. From the 

 numbers present, as determined by dilution platings and other laboratory 

 techniques, they are sometimes assumed to play an important role in soil 

 decomposition processes. As a rule, however, there is little experimental 

 evidence to support such assumptions. 



The descriptions of Penicillia found in the literature up to the begin- 

 ning of Wehmer's work were almost invariably based upon the microscopic 

 examination of preparations made from selected spots in naturally moldy 

 products. Representatives of other genera were usually intermixed. As 

 early as 1890 Sopp reported that he found the current descriptions of 

 Penicillia unsatisfactory, hence turned to laboratory culture as the best 

 hope for a stable nomenclature. 



Culture Media 



The development of artificial culture methods made possible the isola- 

 tion and study of the habits of the individual mold. Along with the 

 academic interest in mold itself, the significance of some of these molds 

 as the active agents of decay, fermentation, or ripening activity gave such 

 studies an increased importance. For the cultivation of Penicillia the 

 media already developed in the study of Aspergilli, yeasts, and bacteria 

 were first utilized. Most species of the group were found to grow readily 

 upon any culture medium used for bacteriological or mycological work. 



Naturally, for organisms growing so readily, students of Penicillium 

 have usually employed formulae already in use in their laboratories, ex- 

 cept as particular purposes called for the development of specific combina- 

 tions. Every kind of medium has, therefore, been used and work has been 

 recorded upon many different nutrients. Certain formulas have, however, 



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