180 CLASSIFICATION OF THE MICliO-OEGANISMS. 



ascertain in investigating a fungus, while on. the other hand 

 this subdivision only indicates the first beginnings of a 

 scientifically correct classification. 



Zopf 's classifi- Another classification of the bacteria has been made by 

 bacteria* ^ Z P f> He extended tne doctrine of pleomorphism which he 

 had observed in the aquatic fungi mentioned above to the 

 other bacteria, original observations, and some made by other 

 observers, having demonstrated in several cases a change 

 of form from cocci into bacilli, threads, and spirilla. Zopf is 

 of opinion that variability of the vegetative forms occurs in 

 all bacteria, and that though in the case of many bacteria 

 the comple'te cycle of forms appertaining to them is not yet 

 known, we may expect that even in the organisms as yet 

 known only in a micrococcal form, thread-forming stages, 

 &c., will yet be discovered. 



Zopf divides the bacteria according to these views into 

 4 groups : 



1. Coccacea?. These are as yet only known in the coccus 

 form. To these the following genera belong: streptococcus 

 (cocci arranged in threads like strings of beads) ; merismo- 

 pedia, tablet cocci (division in two directions, leading to the 

 formation of tablet -like flat layers of cells) ; sarcina, packet 

 cocci (division in three directions, leading to the formation of 

 bale-like colonies) ; micrococcus (division in one direction, the 

 cocci becoming aggregated together in irregular heaps) ; and 

 ascococcus (the heaps of cocci accompanied by marked forma- 

 tion of gelatinous material). 



2. Bacteriaceae. These possess chiefly coccus, rod, and 

 thread forms ; the former may also be absent ; in the latter 

 there is no contrast between base and apex. Threads straight 

 or screw-like. 



Genera: Bacterium, forms cocci and rods, or only rods 

 which are arranged in rows to form ordinary threads ; spore 

 formation absent or unknown. Spirillum, threads screw-like, 

 formed only of rods, or of rods and cocci ; spore formation 

 absent or unknown. Vibrio, threads screw-like, spore forma- 

 tion in the longer or shorter joints. Leuconostoc, forms cocci 

 and rods, spore formation in cocci. Bacillus, cocci and rods, 

 or only the latter in the form of simple or twisted threads ; 

 spore formation present, occurring in rods or in cocci. Glos- 

 tridium, resembles bacillus, but the spore formation occurs in 

 peculiar dilated rods. 



3. Leptothrix. Coccal, rod, and thread forms ; the latter 

 show a contrast between base and apex ; threads straight or 

 screw-like ; spore formation not demonstrated. 



Genera : Crenothrix, threads enclosed in a sheath, cells with- 

 out granules of sulphur; inhabitants of water. Beggiatoa, 



