scinzopiJYTA. 25 



1. To the first division belongs the genus Micrococcus, consisting of small roundish 

 cells which divide in one direction only, and either separate after division or remain 

 strung together like the beads of a rosary. The cells of Sarcina, which lives in the 

 human stomach, on the other hand divide by walls crossing one another in three 

 directions in space and continue united together into small bales, 



2. Among the rod-like forms the genus Bacterium agrees in every respect with 

 Micrococcus, except that the cells are not spherical but clHptic or shortly cylindrical. 



3. In the third division we must distinguish first those forms which have straight 

 filaments. If these filaments are slender, short and rod-like they are named Bacillus, 

 if they are slender and long, Leptothrix, if stouter and long, Beggiatoa ; a form with 

 comparatively large filaments invested with a gelatinous envelope is known as 

 Creiiothrix. Some filaments are branched and are named Cl>uiotItrix\ the mode of 

 branching is as in the Cyanophyceae. 



4. Short rigid filaments with few coils are named Spirillum ; Spi?oc/iat'/c has very 

 slender and not rigid filaments with many coils. 



To these might be added a few more but less characteristic genera ; the species 

 are many in each genus, and are chiefly distinguished by their physiological efifects. 



Two views obtain with regard to the independence of the forms here briefly 

 described. Cohn considers Micrococcus, Bacterium, Bacillus and their allies to be 

 distinct genera, the several species of which exhibit distinct physiological activities. 

 Nageli on the other hand is of opinion that the number of species is small, and that 

 each of these species passes through a definite and somewhat extensive cycle of forms, 

 so that different species may appear in analogous forms and with a similar sphere of 

 operation ; in other words, that one and the same species may appear according to the 

 stage of its development as a Micrococcus, Bacillus, Spirillutn, or CladotJirix\ This 

 latter view finds support in some observations of Cienkowski, who noticed the breaking 

 up of the filaments of C ladothrix and Leptothrix into small portions which then had 

 the form assigned to the genus Bacterium. Still more important are the statements 

 lately published by Zopf^. He observed that the cycle of development in the genera 

 Cladothrix, Beggiatoa and Leptothrix is in fact such as was to be expected according 

 to Nageli's views. An example or two will make this plain. Beggiatoa alba is a very 

 common form with long filaments imbedded in jelly, living chiefly in hot sulphur 

 springs, where they decompose the sulphur compounds in solution in the water and 

 give off sulphuretted hydrogen. These filaments divide into long rods, which divide 

 again into shorter portions, and these by further transverse divisions become Micro- 

 cocci., which swarm and form zoogloea-families. Elongation of the Micrococci leads to 

 the formation of rods, which are either straight {Bacterium) or spiral {Spirilluin) and 

 can also assume the motile condition. After coming to rest they grow into filaments of 

 Leptothrix, which may be bent into stiff spiral forms. Cladothrix also has a micro- 

 coccus-stage, from which shorter or longer rods are evolved, and these grow into 

 leptothrix-like filaments either immediately or after having passed through the stage 

 of swarming movement ; finally the filaments branch in the same way as in the 

 Cyanophyceae, and Cladothrix reappears The filaments consist of longer rods, which 

 separate by transverse division into shorter rods and ultimately into Micrococci. But 

 under certain circumstances the cladothrix-forms as well as the leptothrix-forms 

 may become swarming spiral forms, and these may appear as Spirillum, Vibtio, or 

 Spircchaete. The spiraly-twisted filaments break up into daughter-spirals which 

 swarm by the aid of flagella, and these can themselves again divide. The Microc(Cci 

 may also develope into zoogloea-forms which are branched like a tree. 



' [Ray Lankester Qnait. Journ. Micr. Soc. 1873) pointed out the genetic relationships of Cohii's 

 genera.] 



" Zopf, Ueberd. genetischen Zusammenhnng von Spaltpilzformen (Monatsber. d. Akad. in Berlin, 

 10 Marz 1881). It has yet to be determined whether the course of development as given liy Zopf is 

 common to all the forms of the Schizomycetes. 



