THE SIMPLEST FORMS OF LIFE 



35 



Most bacteria appear, under the microscope, as ex- 

 tremely small, often apparently homogeneous bodies 

 of various shapes — round, oblong, rod-shaped, etc. 

 (Fig. 5). They frequently exhibit active move- 

 ments which are due to the presence of excessively 

 fine cilia. They multiply with extraordinary rapidity 



:3C. 



Fig. 5 (Schizophyta) . — A, the tip of a filament of Oscillaria, one of the 

 Fission Algse (Sohizophyceae). The cell is filled with granular proto- 

 plasm, but no definite nucleus or plastids can he made out. B, part of 

 a filament of Anabsena, a fission alga, showing two sorts of cells; 

 X, one of the " heterocysts " which separate the filament into segments ; 

 C, a water-plant with colonies of a fission alga (Glceotrichia) , gl, grow- 

 ing upon it ; D, Beggiatoa, a form without chlorophyll, allied to Oscil- 

 laria; E-H, different forms of Bacteria (Scliizoraycetes) ; E, typhus 

 germ (Bacillus typhi) ; F, Tetanus bacillus (B, tetani), showing spore 

 formation ; G, cholera bacillus (Micros^ira comma) ; H, spirillum ru- 

 brum ; G and H are stained to show the cilia. (Figs. D-H after Migula.) 



by transverse fission, but may also produce internally 

 special resting-cells, or spores (F). These latter 

 are thick walled, and often capable of enduring an 

 astonishing degree of heat without injury. Organic 

 decomposition is mainly due to the activity of bacteria, 

 and it is unnecessary to dwell upon the various forms 



