18 A MANUAL OF BACTERIOLOGY 



groups or families, which again are subdivided into smaller 

 groups or genera : 



Family I. COCCACE^E. Spherical forms only ; division occurs 



in one or more directions. 



Genus 1. MICROCOCCUS (Staphylococcus). Division in one 

 direction only, but irregular, so that the cocci after division 

 form irregular clusters. 

 Genus 2. STREPTOCOCCUS. Division in one plane, but regular, 



so that the cocci form chains. 



Genus 3. MERISMOPEDIA (Tetracoccus). Division in two direc- 

 tions at right angles to each other, but in the same plane, so 

 that lamellae or plates are formed. 



Genus 4. SARCINA. Division in three directions at right 

 angles to one another and in two planes, so that cubical 

 masses are formed. 

 Genus 5. Ascococcus. Cocci which develop in a gelatinous 



matrix. 



Family II. BACTERIACE.-E. Eods, straight or curved, at some 

 period of the life-cycle, though coccoid and other forms 

 may occur. 

 Genus 1. BACTERIUM. Straight rods ; endospore formation 



does not occur. 

 Genus 2. BACILLUS. Straight rods ; endospore formation 



occurs. 



Genus 3. LEUCONOSTOC. Cocci and rods ; arthospore forma- 

 tion occurs in the coccoid forms. 



Genus 4. CLOSTRIDIUM. The same as bacillus, but the spore- 

 bearing rods are enlarged and club-shaped. 

 Genus 5. SPIRILLUM. Spiral rods ; spore formation does not 



occur. 



Genus 6. VIBRIO. Spiral rods ; spore formation occurs. 

 Family III. LEPTOTRICHE^:. These are unbranching thread 



forms. 



Family IV. CLADOTRICHE^E. These are thread forms showing 

 true but not dichotomous branching. 



There are many features in this classification which 

 are of practical value. The distinction made between 

 a bacterium and a bacillus, for example, is 'convenient. 



