DISTINCTIVE CHARACTERS OF THE BACTERIA. 179 



Bearing a doubtful relation to the fission fungi are : Creno- 

 tlirix, sphserotilus, spiromonas, rabdomoiias ; monas Okenii, 

 Warmingii, vinosa. 



It was frequently stated in the previous edition that this Necessity for 

 classification is in many points impracticable, that many of the^ormer 

 the genera cannot be upheld as independent forms, and that classification, 

 it would have to give place to one more in accordance with 

 practical requirements. In fact it, has become more and more 

 evident in the course of the last few years that certain of the 

 genera up till recently reckoned as independent forms only 

 represent vegetative and colony forms of various species 

 belonging to other groups, and that the presence, of gradual 

 transitional forms greatly increases the difficulty of diag- 

 nosis. Thus a deposit within a tough gelatinous mass which 

 was held to justify the classification under ascococcus occurs 

 more frequently than was formerly supposed, and in bacteria 

 of different vegetative forms (leuconostoc, clostridium, 

 polymym, &c.) Again, sarcina cells are spherical micrococci 

 before the characteristic division into 8 occurs, and often exist 

 for a very long time as isodiametric cells before the division 

 into 4 or 8 is apparent ; other micrococci usually occur as 

 single cells or as diplococci, at times, however, in a meris- 

 mopedia-like arrangement ; hence this character can be em- 

 ployed at the most only in a small group of micrococci. As 

 regards the method of arrangement, clathrocystis closely, re- 

 sembles the genus ascococcus. Further, a distinction between 

 bacterium and bacillus is impossible, because there are too 

 many transition forms which may be placed with as much 

 right in the one class as in the other. The genera leptothrix 

 and streptothrix represent a vegetative form which is seen in 

 many bacilli as an occasional stage of development. Similar 

 difficulties attend the diagnosis between spirillum and spiro- 

 chaste as between bacterium and bacillus. Finally, beggiatoa 

 and cladothrix, on account of their great mutability of form as 

 discovered by Zopf, must be entirely excluded from a classi- 

 fication based on the constancy of morphological characters. 



Cohn, also, has always regarded his classification as a De Bary's 

 provisional one, and one only intended as a general guide till c ^ as sification. 

 a suitable classification is obtained analogous to that of 

 the higher plants, in which special regard is paid to the 

 peculiarities of fructification, and to the natural process of 

 development. Attempts have already been made from the 

 botanical side to form such a classification. Thus Van Tieghem 

 and de Bary make 2 great divisions bacteria which form 

 endospores, and those which form arthrospores ; but this 

 division is of little service for practical purposes, because it 

 is just the mode of spore formation which is most difficult to 



