48 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



"perfect' f-orm. These species are the ' weeds' 1 of the bacterial 

 culture-room, since they cannot be entirely eliminated and often times 

 will survive conditions more severe than the bacteria themselves. 



MOLDS or FERMENTATION.- A few species have acquired special 

 importance by their fermentative action. Certain of these forms are 

 widely distributed and able to utilize other media and conditions. 

 They differ from closely related species of the same genera in the ability 

 to produce special enzymes or especially large amounts of such enzymes 

 as bring about particular forms of fermentation. Certain of these 

 species have been utilized in the manufacture of drinks, of citric acid, 

 in cheese ripening, etc. Others are so adapted to growth under condi- 

 tions of fermentation as to be found constantly in connection with such 

 processes, in which their vigorous growth and fermenting power 

 seriously interferes with control of results. 



PARASITIC MOLDS. Many species of molds have been described 

 as the cause of diseases in man and domestic animals. A few of 

 these forms have been isolated and studied. Some of them attack 

 the lungs, others the kidneys, but the larger number appear 'as the 

 cause of diseased areas (dermatomycoses) of the skin, hair follicles, 

 and external ears, or swellings or malformations of the extremities. 

 Of a large number of forms named from a microscopic determina- 

 tion of their presence in particular lesions, only a few have been 

 adequately characterized and shown to be primary agents in caus- 

 ing the injuries observed. Aspergillus fumigatus, various species of 

 Sporotrichum and Actinomyces, the scalp organisms of herpes and 

 favus appear to be real pathogens. 



GENERIC CONSIDERATION OP GROUPS* 



THE MUCORS OR BLACK MOLDS. The mucors or black molds con- 

 stitute a large group of species belonging to the Phycomycetes or algal 

 fungi whose general characters are a unicellular mycelium, at least in the 

 vegetative stage, and quite generally a well-developed form of sexual 



*The series of forms presented contains representatives of the most common groups as 

 they occur in laboratory cultures, and such as have acquired importance to the worker in 

 bacteriology by participation in processes regularly studied by the bacteriologist. For more 

 complete discussion of the fungi, the student is referred to standard text-books of cryptogamic 

 botany. For discussions of species, Lafar's Technical Mycology includes the groups found 

 associated with the bacteria; for other groups, special botanical literature must be consulted. 



