CHAPTER XLVI 

 HYPHOMYCETES 



THE hyphomycetes or molds interest the bacteriologist chiefly 

 because of the frequency with which they appear as contaminants 

 during bacterial cultivation, and because they play the role of incitants 

 in a few common diseases of the skin and mucous membranes. 



Morphologically they are entirely distinct from and much more 

 complex than the bacteria. To the yeasts they are more closely 

 related, the gap between the two classes being bridged by certain 

 forms often spoken of as "oidia" which, though usually appearing in 

 the budding yeast-form, may occasionally grow out in mycelial threads. 



The characteristic feature of the hyphomycetes as a class is the 

 formation of long, interlacing filaments or threads, known as mycelia. 

 From these, branches come off which are spoken of as "hyphse." Each 

 mycelial thread possesses a well-marked, doubly-contoured sheath or 

 cell-wall and a finely granular protoplasmic cell-body, which, in some of 

 the forms, is multinucleated. 



Two main classes of hyphomycetes are distinguished, the phycomy- 

 cetes, and the so-called higher forms, or mycomycetes. The former class 

 is characterized by the fact that no partitions exist within the mycelial 

 threads or hypha3, the entire meshwork of a single microorganism con- 

 sisting of one multinucleated cell. This group, furthermore, possesses 

 the power of reproduction by both a sexual and an asexual process. 

 The second class, or the mycomycetes, possess a mycelial meshwork 

 which is divided into numerous partitions, and reproduces usually by 

 the asexual process only. 



The process of reproduction, upon the basis of which the separation 

 of groups within this class is determined, is best illustrated by citing a 

 common example of each of the main divisions. > 



As an example of the phycomycetes, the division most commonly 

 met with upon contaminated gelatin plates, or upon exposed and moist 

 organic matter of any description, is the one spoken of as the muco- 



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