HISTORICAL. 



The bacteria are the lowest organisms, situated 

 upon the limit of the two kingdoms, animal and 

 vegetable, and are thus defined by the botanists 

 who have most recently occupied themselves with 

 them : — 



" Cells deprived of chlorophyll, of globular, ob- 

 long, or cylindrical form, sometimes sinuous and 

 twisted, reproducing themselves exclusively by 

 transverse division, 1 living isolated or in cellular 

 families, and having affinities which approach them 

 to the algas and especially to the oscillatoriae." 



But, before arriving at this degree of relative 

 precision, the history of the bacteria has passed 

 through the most diverse vicissitudes. At one 

 time considered as animals, at another taken for 

 vegetables, transported from the algae to the fungi, 

 one author has even gone so far as to refuse to 

 them the nature of living beings. 2 This diversity 

 of opinions is due to the minuteness of their di- 

 mensions and the difficulties with which their ob- 

 servation is surrounded. 



1 Reproduction by spores has been proved to occur in Bacillus subtilis, 

 and it seems altogether probable that other species are reproduced in 

 the same way. — G. M. S. 



2 Polotebnow. 



