MORPHOLOGY AND CLASSIFICATION 1 53 



Two of these generic terms, Spirillum and Spirochjeta, have 

 long been used, and almost in the sense in which they are em- 

 ployed by Migula. Spirillum has frequently been applied to 

 all the Spirillaceffi and especially to those forms which Migula 

 includes in his first three genera, Spirosoma, Microspira and 

 Spirillum. The distinction between Microspora and Spirillum 

 seems of too slight importance to serve as a basis for the formation 

 of two gerera, and indeed 



the same objection exists -^ / j^rj , 



here as in the Bacteriaceae <^^ ^ni J^^v.^ \> -^"'^'O^ 

 to the use of flagella as ^'^ '" """^ ( 



a basis for generic dis- 0/"%^%^^ 



tmctions. ^ PiQ 6g —Types of spirilla. 



Cell division occurs by 

 simple transverse fission in all the spiral bacteria. Endospores are 

 said to be formed by some species. 



The group of spirochaetes has. received much attention in 

 recent years and the propriety of including them in the spirillaeese 

 may be seriously questioned. Many investigators are inclined 

 to regard them as more properly classed with the protozoa than 

 with the bacteria. It is claimed that these forms multiply by 

 longitudinal splitting and not by transverse fission, and this would 

 at once remove them from the Schizomycetes. The observations 

 are still in dispute and there are good observers who regard trans- 

 verse fission as the mode of multiplication. Further study is 

 necessary to settle this important question. It is possible that some 

 of these slender spirals may multiply by both methods, or that 

 one species may divide longitudinally and another transversely, 

 but this does not seem probable. For the present it would seem 

 wise to reserve judgment and avoid encumbering the group with 

 new genera until a definite and final agreement has been reached 

 concerning the exact morphological facts. (See page 368.) 



Structure of Lower Bacteria. — The bacterial cell is enclosed 

 in a relatively stiff cell membrane, which generally retains its form 

 after plasmolysis. Under special conditions of growth many 



