CHAPTER II. 

 BACTERIA AND THEIR PLACE IN NATURE. 



BACTERIOLOGY in the strictest sense is that branch of science 

 which deals with the distribution, morphology, classification, and 

 function of bacteria. However, it is often used more general to 

 include bacteria, yeasts, molds, and protozoa. A better term where 

 all four groups are included is " microbiology." Many of the modern 

 writers use this term. 



Definition of Bacteria. Bacteria are extremely minute, simple, 

 unicellular organisms which multiply with great rapidity, usually 

 by transverse fission, and^are devoid of chlorophyl. Although they 

 contain nuclear material which is usually diffused throughout the 

 cell body in the form of larger or smaller granules, they possess no 

 definite organized nucleus. They are generally accepted as belong- 

 ing to the vegetable kingdom. This is not without some opposition, 

 due to the inherent difficulty of the subject, as is so admirably 

 pointed out by Fischer : ' The terms ' animal' and ' plant' are collec- 

 tive terms invented by laymen to describe familiar living things, 

 insects and elephants, mosses and oak trees, and they date from a 

 time when such minute beings as bacteria were quite unknown. It is 

 therefore as superfluous as it is futile to attempt, as many have done, 

 to detect the distinguishing characters of the 'animal' and the 

 'vegetable' kingdoms among organisms for which these terms were 

 never intended. For this reason, Haeckel and others have proposed 

 to establish a third dominion, that of the Protista, which shall 

 include all those forms in which differentiation has not been pro- 

 nounced on the lines of either animal or plant development. The 

 new group would take up Radiolarians, Flagellata, and Infusoria 

 from the animal side, and the Cyanophycese as well as some low 

 forms of Alga? and Fungi from the plants. The border-line between 

 protista on the one hand and plants and animals on the other is 

 it must be confessed artificial. To these protista, which embrace 

 approximately all those forms of life we commonly call micro- 

 organisms or microbes, the bacteria belong." 



It is generally stated that the plant cell differs from the animal 

 cell by the possession of a firm and well differentiated wall, wholly 

 distinct from the containing protoplasm, whereas the boundary 

 surface of the animal cell is more often an outer layer of the proto- 

 plasm and not separable from it. Moreover, the typical cell wall 



