CHAPTER XVII. 



YEASTS AND MOULDS. 



YEASTS and moulds are grouped in the class of fungi to 

 which the bacteria also belong. They are distinguished 

 from the latter (and from one another) by their mode of 

 reproduction. From the bacteria they also differ in being 

 much larger, as a rule. Their biological requirements 

 are also, generally, much less exacting. 



Between these groups and the average bacterium, the 

 space is bridged by some forms called the higher bacteria, 

 which resemble the moulds* in showing branching. Such 

 are actinomyces (which has been considered immediately 

 after B. tuberculosis), the streptothricae, etc. These are 

 often grouped as trichomycetes, which is regarded as a 

 subdivision of the true moulds. The whole subject is at 

 present uncertain and confused. Foulerton, in his Milroy 

 Lectures (Lancet, 1910, Vol. i., p. 551 on) urges the view 

 that the micro-organisms variously called tubercle bacilli, 

 actinomyces, cladothrix nocardia, oospora, and strepto- 

 thrix, belong to one family of moulds or hyphomycetes. 



In clinical medicine and pathology the term " mycoses " 

 is used (following Virchow) to denote all the affections 

 produced by filamentous and budding fungi, and this term 

 associated with the seat of the lesion has given rise to such 

 terms as dermatomycosis, otomycosis, etc. On the other 

 hand, such terms as actinomycosis, saccharomycosis, 

 blastomycosis, aspergillosis, sporotrichosis, etc., are used. 



All the members of these groups may be considered as 

 facultative parasites, parasitic life being unnecessary to 

 their cycle of evolution, as their proper existence is a 

 saprophytic one. The parasitism is, in their case, simply 

 a phenomenon of adaptation. 



Being destitute of chlorophyll, they do not need light, 

 and grow luxuriantly in the dark. They vary much in 

 their temperature requirements, a few growing well at 



