3.32 I IOTA NY r.uir n 



soil, in the atmosphere, or in the bodies of dead or living plants and 

 animals. They are often termed Fission-Fungi, or Schizomycetes, 

 since the multiplication of the unicellular forms takes place by a 

 division into two and the separation of the segments. This mode 

 of multiplication is also found in other unicellular plants. 



The cells of the Bacteria arc surrounded by a thin membrane, and 

 contain a protoplasmic body, which is usually colourless, and can 

 be made to contract away from the membrane by plasmolysis. 

 The protoplasm may contain one or more vacuoles. One or several 

 granular structures are also present in the protoplast; these so-called 

 chromatin bodies may be deeply coloured by stains, and have been 

 regarded as nuclei by various authors. Since, as yet, undoubted karyo- 

 kinetic division has not been observed in these bodies, the presence of 

 nuclei in the bacterial cell cannot be regarded as certainly established. 



For the most part the Bacteria are extraordinarily minute organ- 

 isms, and probably include the smallest known living beings. The 

 spherical cells of the smallest forms are only O'OOOS mm. in 

 diameter ; the rod-shaped cells of the tubercle bacillus are only 

 0'0015-0'004 mm. long, while the transverse diameter of most 

 species is about O'OOl mm. 



The simplest form of Fission-Fungi are represented by minute 

 spherical cells, COCCI. Forms consisting of rod-shaped cells are 

 designated BACTERIUM or BACILLUS. Rod-shaped forms with a slight 

 spiral curvature are called VIBRIO, and those more strongly curved 

 SPIRILLUM. Straight filamentous forms are termed LKPTOTIIJ:IX, 

 spirally wound filaments, SPIROCHAETE. In the highest stage of their 

 development the Fission-Fungi consist of cell filaments exhibiting 

 false branching. The unicellular cocci, rod -shaped forms, and 

 vibrios may also remain united in chains after the cell-division. 

 Frequently the cell -membranes undergo a mucilaginous swelling, 

 the cells or cell-rows being embedded in the gelatinous mass. This 

 stage of development is termed ZOOGLOEA. 



Many Bacteria are motile. Their independent movements arc due 

 to the vibration and contraction of fine protoplasmic cilia. These 

 flagella, according to A. FISCHER, are either distributed over the whole 

 surface of the cells (peritrichous) (e.g. Bacillus subtilis, Fig. 254 a, d; 

 Bacillus typlii, Fig. 252 c; Bacillus tetani, Fig. 257 e), or they spring 

 from a single point either as a single flagellum (monotrichous) or 

 as a group (lophotrichous). A single, polar flagellum occurs in 

 niirio cholerae (Fig. 252 a) ; a polar terminal tuft of flagella in Spiril- 

 lum a in/ ula (Fig. 252 b, d) ; a lateral tuft in the swarm-spores of 

 Cladotlirix (Fig. 253). The ciliary tufts may become so closely inter- 

 twined as to present the appearance of a single thick flagellum, The 

 cilia are never drawn within the body of the cell, but undergo 

 dissolution before the formation of spores takes place, or under 

 unfavourable conditions (Fig. 252 e). 



