18 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



they contain no chlorophyll ; they all possess an envelope or 

 capsule consisting probably of cellulose or allied substances. 

 For these various reasons they are classed among the fission 

 fungi, and from their method of reproduction are known as 

 schizomycetes. 



They are further divided according to their main differences 

 in form into the following subdivisions : — 



1. Coecaceae, round cells ; 



2. Bacteriaceae, rods and threads ; 



3. Leptotricheae ) 



4. Cladotricheae J ^'^^^"^ bacteria. 



Yeasts (Fig. 3, II.).— These are closely aUied to the 

 bacteria, differing mainly in their method of reproduction. 

 This consists in the formation of small daughter cells or buds 

 which are extruded from the parent cell, a process known as 

 budding. Their chemical functions are also more complex, 

 a single yeast cell being able to bring about a number 

 of different chemical changes. As they are mainly capable 

 of growing in a saccharine medium, they are known generally 

 as saccharomycetes. The characteristic form of yeast cells 

 with buds is shown in Fig. 3, II. 



Moulds (Fig. 3, III.).— These are still more highly organ- 

 ised than the bacteria or yeasts ; they are sporing organisms. 

 The spores or conidia give rise to long threads of cylindrical 

 cells forming a network known as mycelia. From these cells 

 special seed-bearing organs known as hyphae or thalli develop. 

 From these organs the moulds derive their general name of 

 hyphomycetes. 



Thus a mould which at first has a fine thread-like appear- 

 ance, on further growth will be seen to be covered with minute 

 dots, which are often of a darker colour than the myceha; 

 these on microscopical examination will be found to be the 

 hyphae ; in the case, e.g., of aspergillus niger the hyphae are 



