206 



PROTOZOA. 



1. The ScliizomyGtMaa)* (Bacteria) are small globular or rod-shaped bodies 

 which are found in decaying matter, and are especially numerous on the surface 

 of putrefying fluids, where they give rise to a slimy film (fig. 148). They are 

 most nearly allied to the fungus of yeast, with which they also agree in their 

 manner of nourishment, in that they make use of ammonia and organic com- 

 pounds containing carbon. Like the yeast fungus they excite and maintain 

 the fermentation or, as may happen, putrefaction of organic matter by with- 

 drawing its oxygen or by attracting oxygen from the air (reduction or oxyda- 

 tion ferments). But they are clearly separated from the fungi by their deve- 

 lopment, for they increase by dividing into two ha-lct's, while the yeast fungus 

 (Saccharomyces, Hormiscium) forms buds which separate off as spores. The 

 transverse division takes place, after the cell has become elongated, by a con- 

 striction of the protoplasm and by the secretion of a cross partition wall. The 

 daughter-cells either divide at once, or remain united and produce chains of 

 Bacteria (filiform Bacteria) by afresh fission. Sometimes the successive genera- 

 tions of cells remain connected by a gelatinous substance, and so produce irre- 

 gular shaped gelatinous masses (zoogloea). Sometimes they become free and 

 arc dispersed in swarms. They may also settle on the bottom in the form of a 



FIG. 148. Schizomycetcs (sifter F. Cohn). a, Micrococcus. b, Bacterium termo, bacteria of 

 putrefying fluids, both in the motile and zoogloea form. 



granular precipitate, as soon as the nourishment in the fluid is exhausted. The 

 greater number have a motile and a motionless stage ; in the first they rotate 

 themselves about their long axis, but are also able to bend and extend, but never 

 to serpentine. Their activity seems to be connected with the presence of 

 oxygen. 



Owing to the absence of sexual reproduction, the division of Bacteria into 

 genera and species is beset with such difficulty that we must content ourselves 

 with establishing, in an artificial fashion, form species and physiological species 

 and varieties without always being able to demonstrate their independence. 

 F. Cohn distinguishes four groups : (1) Globular Bacteria, Micrococcus 

 (Mona* and My coder ma) ; (2) Rod Bacteria (Bacterium) ; (3) Filiform 

 Bacteria (Bacillus and Vibrio) ; (4) Spiral Bacteria (Sjnrillum and 

 Sjriroch&ta). 



The Globular Bacteria are the smallest forms, and only exhibit molecular 

 movements. They cause various forms of decomposition, but not putrefaction. 



* F. Cohn, " Bcitrage zur Biologic tier Pflanzen." Heft 2 and 3, 1872 and 

 1875. " Untcrsuchungen iiber Baktcricn," 1, 2, and 3 (Bacterium termo). Com- 

 pare further the works of Ebcrth and Klebs. 



