1 6 MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



phytic species has been recognized by the development in recent years 

 of the literature of plant pathology (phytopathology). These cannot 

 be considered in this work. 



SPECIFIC CONSIDERATION OF MOLDS. 



A few species are found to grow very constantly in the same situations 

 as bacteria. These are associated with forms of decay, fermentation, 

 or disease, either as primary or secondary causes. They thus become 

 important to the bacteriologist who studies them by the same methods 

 as bacteria. These species belong to widely scattered groups of fungi, 

 so that species found under the same conditions frequently differ greatly 

 in appearance. The common term, molds, is applied collectively to 

 these organisms, though no sharp limits can be set to the use of the term. 

 Physiologically these species can be considered in three series: 



COSMOPOLITAN SAPROPHYTES. Certain species are capable of 

 growing within very wide limits of temperature and of composition of 

 substrata. Many of these have accompanied man everywhere and are 

 constantly found upon every kind of putrescible matter, especially as the 

 causes of fermentation or decay in food. Their spores (conidia) are 

 produced in countless numbers, and are so light that they float in air 

 currents and are carried by contact in every conceivable manner by 

 animals and by man. The life cycle from spore to spore is frequently 

 very short, often being completed in twenty-four hours or less. Many 

 of these forms are propagated for an indefinite number of generations by 

 asexual spores or conidia, while for some of them no sexual-fruiting form 

 is known. These species are the "weeds" of the bacterial culture-room, 

 since they cannot be entirely eliminated and will survive, as a rule, 

 conditions more severe than the bacteria themselves. 



MOLDS OF FERMENTATION. A few species have acquired special 

 importance by their fermentative action. In most cases these forms 

 are widely distributed and able to utilize other media and conditions 

 also. They differ from closely related species of the same genera in the 

 ability to produce special enzymes or specially 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 

 conditions of fermentation as to be found constantly in connection with 



