Bacteria 35 



cocci remain attached to one another like a string of beads, the 

 organism is described as a streptococcus. 



Cocci commonly occur in irregular groups having a fancied re- 

 semblance to bunches of grapes. Such are called staphylococci, and 

 most organisms not finding a place in the varieties already described 

 are so classed. 



Cocci associated in globular or lobulated clusters, incased in a 

 resisting gelatinous, homogeneous mass have been described by 

 Billroth as ascococcus. Cocci solitary or in chains, surrounded by an 

 incasement of almost cartilaginous consistence, have been called 

 letcconostoc. 



^ 



Fig. 3. — Diagram illustrating the morphology of the bacilli: a, b, c, Various 

 forms of bacilli; d, e, bacilli with flagella;/, chain of bacilli, individuals distinct; 

 g, chain of bacilli, individuals not separated. 



Bacilli. — Better known, if not more important, bacteria consist of 

 elongate or "rod-shaped forms," and bear the name bacillus (a rod). 

 These present considerable variation of form. Some are ellipsoid, 

 some long and slender. Some have rounded ends, as Bacillus 

 subtUis; others have square ends, as B. anthracis. Some are large, 

 some exceedingly small. Some always occur singly, never uniting 

 to form threads or chains; others are nearly always so conjoined. 



The bacilli divide by transverse fission only, so that the only 

 peculiarity of arrangement is the formation of threads or chains. 

 In the older writings, short, stout bacilli were described under the 

 generic term bacterium. Migula now employs the term to include 

 only bacillary forms without flagella. A pseudomonas is a bacillary 



Fig. 4. — Diagram illustrating the morphology of the spirilla: a, b, c, Spirilla. 



form with polar flagella. Some of the flexile bacilli have sinuous 

 movements resembling the swimming of a snake or an eel, and are 

 sometimes described as vibrio; but this name also has passed into 

 disuse, except in France. 



Spirilla. — If a rod-shaped bacterium is spirally twisted and re- 

 sembles a corkscrew, it is called spirillum. The rigid forms without 

 flagella are known as spirosoma; rigid forms with flagella, spirilla 

 and microspira. 



