44 BACTERIA. 



of development of any species, and he has determined that 

 both form and developmental series must be used in drawing 

 up a classification. 



ZOPF'S CLASSIFICATION. 



Group i. COCCACE^;. These are as yet only known in the coccus form. 

 To these the following genera belong : 



1. Streptococcus (cocci arranged in threads like strings of beads). 



2. Merismopedia, tablet cocci (division in two directions, leading to the 



formation of tablet-like flat layers of cells). 



3. Sarcina, packet cocci (division in three directions, leading to the 



formation of bale-like colonies). 



4. Micrococcus (the cocci become aggregated in irregular heaps). 



5. And ascococcus (the heaps of cocci accompanied by marked formation 



of gelatinous material). 



Group 2. BACTERIACE^:. These possess chiefly coccus, rod, and thread 

 forms ; the former may be absent ; in the latter there is no distinction 

 between base and apex. Threads straight or screw-like. Genera : 



1. Bacterium, forms cocci and rods, or only rods which are arranged in 



rows to form ordinary threads ; spore formation absent or unknown. 



2. Spirillum, threads screw-like, formed only of rods, or of rods and 



cocci ; spore formation absent or unknown. 



3. Vibro, threads screw-like, spore formation in the longer or shorter joints 



4. Leuconostoc, forms cocci and rods, spore formation in cocci. 



5. Bacillus, cocci and rods, or only the latter in the form of simple or 



twisted threads ; spore formation present. 



6. Clostridium, the bacillus form in which the spore formation occurs in 



peculiar enlarged rods. 



Group 3. LEPTOTHRICHE^. Coccal, rod, and thread forms; the latter 

 show a distinction between base and apex ; threads straight or screw-like, 

 spore formation not demonstrated. Genera : 



1. Crenothrix, threads jointed and enclosed in a sheath, cells contain no 



sulphur granules ; inhabit water. 



2. Beggiatoa, threads thicker than Crenothrix, indistinctly articulated, 



cells contain sulphur granules ; inhabitants of water. 



3. Phragmidiothrix, threads without sheaths, successive divisions very 



numerous ; cells contain no sulphur ; inhabit water. 



4. Leptothrix, threads with or without sheaths, divisions not very 



numerous or well marked ; cells devoid of sulphur. 

 Group 4. CLADOTHRICHE^E. Show coccus, rod, thread, and spirillar 

 forms. The thread form is provided with a sheath, well-marked segments 

 and pseudo-branches. Spore formation not yet demonstrated. Genus : 

 Cladothrix. 



Winter and Rabenhorst's classification, though very con- 

 venient, is far from scientific, but it serves especially well 

 for the classification of micro-organisms that are found in 

 disease, as these, as met with in their host, usually correspond 

 to one stage only of Zopf 's developmental cycle of any special 

 organism. 



