Chapter IV 

 CULTIVATION AND EXAMINATION 



An Aspergillus occurring upon a natural substratum may frequently be 

 identified as to group from the original material if it belongs to one of the 

 large and well-marked groups. Among members of the same group, how- 

 ever, differences in the nature and composition of the substratum produce 

 marked contrasts in colony appearance, quantity of growth, coloration, 

 measurements of fruiting structures, and in the appearance of conidiophores 

 and conidial masses. Many Aspergilli can be identified as to group from 

 dried herbarium materials, but the process of drying generally changes the 

 colors materially and renders the hyphal masses so fragile that the morpho- 

 logical details necessary for identification inside a particular group are often 

 obliterated or made difficult to interpret. Although accurate placing of 

 such materials is sometimes possible, a much more satisfactory identifica- 

 tion may be reached by transferring fresh material to culture media of 

 known composition, followed by purification of the cultures so that they 

 present single species or strains for intensive study. 



Two types of material for identification are regularly encountered by one 

 undertaking a study of the Aspergilli: (1) the culture already isolated by 

 another worker, and (2) the moldy substratum with its natural flora of 

 micro-organisms often representing several or many species, including 

 miscellaneous molds, bacteria, actinomycetes, and even protozoa and other 

 forms. In either case, the final decision as to the proper name of an 

 Aspergillus must usually be sought in fresh cultures made by the one re- 

 sponsible for identification. 



Classification within the genus has become so dependent upon observa- 

 tion in pure culture that the whole subject of laboratory cultivation, includ- 

 ing favorable substrata, culture making, and culture handling needs to be 

 considered. 



CULTURE MEDIA 



Pure culture upon known substrata is almost essential to the identification 

 of Aspergilli. Since the morphological responses to diverse nutrients, and 

 especially to the stimulus of mixtures of other molds and bacteria growing 

 with any particular species, is great, the study of each strain or species in 

 pure culture in media of known composition is practically necessary. 



Aside from Raulin's group in Paris, most of the early culture work with 

 Aspergilli was carried through upon so-called natural media. DeBary and 



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