146 GENERAL BIOLOGY OF MICRO-ORGANISMS 



the bacteriaceae and the form of the spore-bearing cell differs 

 for different species and is fairly constant for any one species. 



FIG. 65. Position of spores; resultant forms (diagrammatic), a, Median 

 spores; b, intermediate spores; c, terminal spores; 20,, b, c, change in form of cells 

 due to the presence of the spore; 20, clostridium; 20, drum-stick form. (After Novy.} 



The spore, which is always single, may be located at the center of 

 the cell, median spore, or at the end, terminal spore, or 

 at an intermediate point. The spore-bearing cell may retain 

 its normal outline or it may be bulged by the spore. The cell 

 containing a median spore with bulging is called a clostridium; 

 one with terminal spore with enlargement of the cell is spoken 

 of as a drumstick or sometimes as a plectridium. 



Spiral Bacteria. The screw-shaped bacteria, Spirillacea, have 

 been subdivided into four genera by Migula. The genus Spiro- 

 soma includes those spirals which are rigid and without motility. 

 Motile cells possessing one, two or three polar flagella are classes 

 in the genus Microspira; while those possessing more than three 

 are put in the genus Spirillum. The genus Spirochaeta includes 

 the slender flexuous forms of spirals. 



SPIRILLACE^E Cells circular in cross-section but 



curved to form a spiral or segment of a spiral. 

 Spirosoma Cells rigid, without flagella, motionless. 

 Microspira Cells rigid, motile, with i to 3 polar flagella. 

 Spirillum Cells rigid, motile, with polar tufts of flagella. 

 Spirochaeta Cells slenders, flexuous, motile. 

 Two of these generic terms, Spirillum and Spirochaeta, have 

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

 ployed by Migula. Spirillum has frequently been applied to 



