MORPHOLOGY AND CLASSIFICATION 147 



all the Spirillaceae and especially to those forms which Migula 

 includes in his first three genera, Spirosoma, Microspira ancf 

 Spirillum. The distinction between Microspora and Spirillum 

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

 of two genera, and indeed the same objection exists here as in 

 the Bacteriaceae to the use of flagella as a basis for generic 

 distinctions. 



Cell division occurs by simple transverse fisson in all the spiral 

 bacteria. Endospores are 



said to be formed by some . / 



species. $fr ,Tu ^ \f 



The group of spiro- V 

 chaetes has received much O/V^W^ 



attention during the past FlG . 66. Types of spirilla. 



decade and the propriety 



of including them in the spirillaceae 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 transverse fisson as the mode of 

 multiplication. Further study is necessary to settle this impor- 

 tant 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 judg- 

 ment and avoid encumbering the group with new genera until a 

 definite' and final agreement has been reached concerning the 

 exact morphological facts. (See page 353.) 



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 

 forms of bacteria become enclosed in a gelatinous capsule. This 

 seems to be a viscid material secreted by the cell through the cell 



