28 THE FUNDAMENTAL PRINCIPLES. 



to be animalcules, and were accepted as such until the middle 

 of the nineteenth century, when F. Cohn classed them as 

 belonging^ to the vegetable kingdom, and listed them among 

 the fungi, making of them the third variety of fungi, the 

 schizomycetes or cleft fungi ; the other two being the saccharo- 

 mycetes or sprouting fungi (the yeast plant), and the hyphomy- 

 cetes or mucorini (the moulds). 



THE CLASSIFICATION OF COHN FOR BACTERIA. 



This, as just given, is accepted to-day by all authori- 

 ties, though it is open to criticism. Although it is true that 

 the great majority of these organisms like the fungi possess 

 no chlorophyl, and are unable, like other vegetables, to obtain 

 their nourishment from the carbon dioxide and nitrogen of 

 the atmosphere, but, on the contrary, like animals, require 

 higher carbohydrate and nitrogenous substances, which they 

 decompose into their primitive elements for their subsistence. 

 A few of them, however, possess some plant coloring-matter, 

 and some seem able to thrive in a simple saline solution from 

 which absolutely no nitrogen is to be obtained. 



THE DEFINITION OF " BACTERIA." 



The proper name therefore for these organisms, and the 

 one generally adopted, is bacteria, which is the plural of the 

 Latin substantive bacterium. They may be defined as fol- 

 lows : Unicellular vegetables of low organization, devoid of 

 chlorophyl (plant color ing -matter), and multiplying by fission. 



The bacteria cells consist of a cell-membrane and protoplasm, 

 which latter is sometimes clear and sometimes granular, but 

 with no nuclei. The cell-membrane is a firm, tough envelope, 

 very much like cellulose, which occasionally in some bacteria 

 becomes viscid and gelatinous in its outer layers, forming a sort 

 of bright halo around the bacteria, called a capsule. This 

 gelatinous matter occasionally serves to bind two or more 

 bacteria together, and gives to them quite a characteristic 

 grouping which helps to distinguish them from others. In 

 some instances the membranous envelope interferes consid- 



