THE YEASTS -THE-MOULDS. 217 



THE YEASTS. 



The yeasts, on account of their multiplication by budding, 

 form a distinct class among fungi. They are widely sepa- 

 rated in their morphology from the schizomycetes or cleft 

 fungi (bacteria), while between them and the hyphomycetes or 

 mucorini (the moulds) there are occasional features of simi- 

 larity. This is especially shown in the occasional formation 

 in certain yeasts of hyphse and mycelia. The yeasts ordi- 

 narily consist of cells averaging 15 /;. in length and 10 n in 

 width, and consisting of a cell membrane and protoplasm con- 

 taining vacuoles and highly refractile globules and nuclear 

 granules. Multiplication takes place by the extrusion of the 

 cell membrane of the mother-cell to form the daughter-cell 

 (budding). For a time the maternal protoplasm continues to 

 enter the daughter-cell freely and nourish it until the grad- 

 ual narrowing of the connecting isthmus between the two is 

 cut off, as the daughter-cell reaches maturity. 



Yeasts are more of interest in the trades, but the reports at 

 different times by Busse, Zinnser, and others of human infec- 

 tion by the Saccharomyces hominis have naturally drawn the 

 attention of medical men more strongly to the subject. 



THE MOULDS. 



The hyphomycetes or moulds constitute the third division 

 of the fungi, as suggested by Cohn (p. 28). They occur ex- 

 tensively in nature and constitute a frequent source of con- 

 tamination in cultures, on which they appear as a fluffy white 

 light layer, having the appearance of adherent cotton or wool. 

 This layer, if examined, will be found to consist of a number 

 of interlacing threads or mycelia, from which larger branches, 

 called hyphcBj extend to terminate in bulbous extremities called 

 sporangia. These latter contain the small rounded spores, 

 which escape when the sporangia burst at maturity to develop 

 into new mycelia, if the environment is suitable. This method 

 constitutes the asexual type of reproduction, and is common 

 both to the higher class of moulds, the iiiycomycetes, and to 



