14 BACTERIA 



tinctive characteristics as regards the contents inside the 

 capsule which call for mention. Sulphur occurs in the Beg- 

 giatoa which thrive in sulphur springs. Starch is commoner 

 still. Iron as oxide or other combination is found in several 

 species. Many are highly coloured, though these are generally 

 the "innocent" bacteria, in contradistinction to the disease- 

 producing. A pigment has been found which is designated 

 bacterio-purpurin. According to Zopf, the colouring agents 

 of bacteria are the same as, or closely allied to, the colouring 

 matters occurring widely in nature. Migula holds that most 

 of the bacterial pigments are non-nitrogenous bodies. There 

 are a very large number of chromogenic bacteria, some of 

 which produce exceedingly brilliant colours. Among some 

 of the commoner forms possessing this character are Bacillus 

 et micrococcus violaceus (violet) ; B. ct M. aurantiacus 

 (orange) ; B. et M. luteus (yellow) ; M. roseus (pink) ; many 

 of the Sarcince ; B. aureus (golden-yellow); B. fluorescens 

 liquefaciens et non-liquefaciens (green) ; B. pyocyaneus (green) ; 

 B. prodigiosus (blood-red). 



Motility. When a drop of water containing bacteria is 

 placed upon a slide, a clean cover glass superimposed, and 

 the specimen examined under an oil immersion lens, various 

 rapid movements will generally be observed. These are of 

 four kinds: (i) A dancing stationary motion known as 

 Brownian movement. This is molecular, and depends in 

 some degree upon heat and the medium of the moving 

 particles. It is non-progressive, and is well known in gam- 

 boge particles. (2) An undulatory serpentine movement, 

 with apparently little advance being made. (3) A rotatory 

 movement, which in some water bacilli is very marked, and 

 consists of spinning round, with sometimes considerable 

 velocity, and maintained for some seconds or even minutes. 

 (4) A progressive darting movement, by which the bacillus 

 passes over some considerable distance. 



The conditions affecting the motion of bacteria are but 



