40 Structure and Classification of Micro-organisms 



Aciinomyces— The chief characterization of the organisms of this 

 group is a clavate expansion of the terminal ends of radiating fila- 

 ments. These are seen in sections of diseased tissues containing the 

 organisms, but rarely are well shown in the artificial cultures. For 

 further particulars of these organisms see Actinomyces bovis, etc. 

 THE YEASTS, OR BLASTOMYCETES 



The organisms of this group are sharply separated from the 

 bacteria by their larger size, elliptic form, and by multiplication by 

 gemmation or budding. 



Each organism is surrounded by a sharply defined, doubly 

 contoured, highly refracting, transparent cellulose envelope. Com- 



Fig. g.' — Blastomycetes 'dermatitidis. Budding forms and mycelial growth 

 from glucose agar (Irons and Graham, in "Journal of Infectious Diseases"). 



monly each cell contains one or more distinct vacuoles. When 

 multiplication is in progress, smaller and larger buds are formed. 



The yeasts, of which Saccharomyces cerevisias may be taken as 

 the type, are active fermentative organisms, quickly splitting the 

 sugars into CO2 and alcohol, and are largely cultivated and used 

 in the manufacture of fermented liquors and bread. They grow well 

 in fermentable culture-media and most of them also grow upon the 

 ordinary laboratory culture-media. Many varieties, some of 

 which produce red or black pigment, some no pigment at all, are 

 known. They play very little part in the pathogenic processes. 

 Burse has observed a case of generalized fatal infection caused by an 

 yeast that he calls Saccharomyces hominis. Gilchrist, Curtis, 

 Ophlils, and others have seen localized human infections by blasto- 

 mycetes. (See Blastomycetic dermatitis.) 



Ashford* has described a pathogenic yeast to which Andersonf has 



* "Journal of Tropical Diseases and Preventive Medicine," 1915, in, No. i, 

 p. 32. 



t "Journal of Infectious Diseases," 1917, xxi, No. 4, p. 341. 



