CLASSIFICATION 



class comprises, with few exceptions, forms without chlorophyll, 

 while the second comprises only forms with chlorophyll. 



CLASS I. BACTERIA (SCHIZOMYCETES) 



The Bacteria comprise the simplest of all known organisms, as 

 well as the smallest; but nevertheless they are of the highest 

 importance in the economy of nature, the existence of all the higher 

 forms of life being more or less directly dependent upon them. 



Cell-structure of Bacteria. Owing to the very small size of most Bacteria, 

 it is excessively difficult to make out the structure of the cell, and there is much 

 difference of opinion as to what the cell-structure really is. In some of the 

 larger forms, e.g. Beggiatoa, structures similar to those visible in the Schizo- 

 phyceae have been demonstrated, but it is probable that these larger forms 

 are more nearly related to the latter than they are to the true Bacteria. In 

 many of the smaller Bacteria the young cells may appear perfectly homogene- 

 ous, except for the presence of a limiting cell-membrane, which, however, only 

 in rare instances, e.g. Bacterium Pasteurianum, shows the cellulose reactions. 

 The protoplasm usually stains strongly, and certain observers have considered 

 that the whole represents a nucleus, and is comparable to the "central-body" 

 in the Schizophyceae. It has, however, been demonstrated that a vacuole may 

 arise in the protoplast, which is hardly 

 consistent with its being a nucleus. 

 Granules, staining more deeply than the 

 rest of the protoplast, are usually present, 

 and may perhaps represent the nuclear 

 substance, which is not segregated into 

 a definite nucleus. In short, the evi- 

 dence at present available is against the 

 existence, in the bacterial cell, of an 

 organized nucleus. 



The cells may be isolated, or they may 

 form colonies of characteristic form and 

 color, which make it possible to recognize 

 at once certain species. Thus a common 

 species, Micrococcus prodigiosus, forms 

 small blood-red specks on moist bread, 

 and the colonies grown in culture-tubes, 

 or on gelatine, always behave in a con- 

 stant manner (Fig. 52). 



Movements 



Many Bacteria exhibit active 

 movements, due to extremely deli- 

 cate cilia, which may be attached 

 either to the ends of the cells, or 

 may grow out from all parts of the 

 surface. By contracting the cell- 

 contents, it is readily seen that the 



FIG. 51. A, Bacillus typhi (Typhus- 

 germ) (X 1000). B, B. tetam (Tet- 

 anus-germ) , showing spore-forma- 

 tion ( X 1000) . C, Microspira comma 

 (Cholera-germ), stained to show the 

 flagellum (X 1000). D, Bacillus 

 subtilis, showing the cilia (X 1000). 

 E, Spirillum undula. F, Bacillus 

 amylobacter, germination of the 

 spores (X 1000). (Figs. A, B, C, F, 

 after MIGULA.) 



