36 BIOLOGY AND TECHNIQUE 



classification which can in any way be regarded as final. It is, there- 

 fore, quite impossible to classify the bacterial varieties or species on any 

 basis which can hope to satisfy all the demands of scientific accuracy 

 and it is necessary to resort to the expedient of utilizing some one 

 characteristic which remains constant for the individual genus and to 

 base upon this an attempt at grouping. When bacteria were first dis- 

 covered, and for many years following, numerous observers contended 

 that the form of the microorganism observed was not a constant one 

 for each genus, but that cocci could be converted into bacilli or spirilla 

 according to environmental conditions. It was Cohn 1 who, in 1872, 

 first recognized the constancy of the morphology of bacteria and es- 

 tablished, upon morphological basis, a classification which, with minor 

 changes, has been retained until the present day. Such classifications 

 can not, however, be regarded as anything more than a convenient 

 make-shift pending the day when the finer structure and true biological 

 relations of the various bacteria shall have been more accurately inves- 

 tigated. The scheme most commonly accepted at present is the one 

 given below, proposed by Migula 2 : 



Bacteria (Schizomycetes). Fission fungi (chlorophyll free), cell division in one, 

 two, or three directions of space. Many varieties possess power of form- 

 ing endospores. Whenever motility is present, it is due to flagella, or, 

 more rarely, to undulating membranes. 



FAMILY I. COCCACE^E. Cells in free state spherical. Division in one, two, 



or three directions of space, by which each cell divides into two, four, or 



eight segments, each of which again develops into a sphere. Endospore 



formation rare. 

 Genus I. Streptococcus. Cells divide in one direction of space only, for 



which reason, if they remain connected after fission, bead-like chains may 



be formed. No organs of locomotion. 

 Genus II. Micrococcus (Staphylococcus). Cells divide in two directions 



of space, whereby, after fission, tetrad and grape-like clusters may be 



formed. No tfrgans of locomotion. 

 Genus HI. Sarcina. Cells divide in three directions of space, whereby, 



after fission, bale-like packets are formed. No organs of locomotion. 

 Genus IV. Planococcus. Cells divide in two directions of space, as in 



micrococcus, but possess flagella. 



1 Cohn, "Beitrage zur Biol. d. Pflanzen," Heft 1 u. 2, 1872. 



2 Migula, "System d. Bakt.," Jena, 1897. 



