52 BACTERIOLOGY. 



creatures with which we have acquaintance, being visible 

 only when very highly magnified. In order that some 

 conception of their microscopic dimensions might be 

 formed, it has been computed that of the average size 

 bacteria about thirty billion would be required to weigh 

 a gramme, and that about one billion seven hundred 

 million of the small spherical forms might readily be 

 suspended in a drop of water. 



THE CLASSIFICATION OF BACTERIA IN FAMILIES. 



The classification of bacteria into families, genera, 

 and species has been a subject of much labor and dis- 

 cussion. It is impossible, on account of limited knowl- 

 edge of certain species, to make the classification of the 

 bacteria accurate. 



The basis for modern systems of classification has 

 been the most pronounced morphologic characters. The 

 system of classification which has proven of greatest 

 value is that projx>sed by Migula, in Engler and Prantl's 

 Die Nat'iirliehen Pflanzenfamilien, 1896, and elaborated 

 in his System der Eakterien, 1900. The nomenclature 

 employed in the description of the bacteria is that of 

 Migula. 



SCHIZOMYCETES. Bacteria. Unicellular, chloro- 

 phyll-free organisms which reproduce by division into 

 one, two, or three directions of space. Sexual repro- 

 duction is absent. Many species develop endogenous 

 spores. Motility, occurring in some genera, is due to the 

 presence of flagella ; in Beggiatoa and Spirochata the 

 motile organs are unknown. 

 I. ORDER : EUBACTERIA. 



Cells without central nuclei, sulphur, and bacterial 

 purpurin ; colorless or only feebly colored. 



