REPRODUCTION OF BACTERIA 263 



spores are frequently located in special parts of the cell, giving 

 the spore-forming individuals a characteristic appearance, as 

 in Bacillus tetani, where they occupy a dilation of one end 

 (Fig. 145, a). In certain forms (e.g. Bacillus amylobacter) more 

 than one spore may be developed by each individual. Bacterial 

 spores are often very resistant to extremes of temperature, and 

 can indeed in some cases (e.g. Bacillus subtilis) withstand pro- 

 longed boiling. 



Most sorts of Bacteria live a free life in water, earth, etc. 

 Many exert a very beneficial action in promoting decay and main- 



FIG. 144. Various Bacteria (magnified about 1,000 times), a, Staphylo- 

 coccus aureus ; b, Streptococcus pyogenes ; c, Pneumococcus ; d, Bacillus 

 anthracis ; e, B. typhosus ', f, B. tetani ; g, Microspora comma ; h, Spi- 

 rillum of relapsing fever (possibly Protozoal) ; k, Spirillum rubrum ; 

 /, Pseudomonas spp. j represents a blood corpuscle on the same scale, 

 and the line below, the width of a fine human hair, or about half the 

 thickness of a sheet of newspaper. (a-h from Muir and Ritchie ; 

 h-l after Engler and Prantl.) 



taining the circulation of nitrogen and carbon dioxide in nature, 

 whilst a small number are extremely harmful, living as parasites 

 on higher animals and plants, and causing such diseases as 

 typhoid, cholera, plague, etc. Whilst some, such as Bacillus 

 subtilis, which is found in infusions of hay, etc., require a free 

 supply of oxygen (aerobic species), others, such as the organism 

 responsible for lock-jaw (Bacillus tetani), will grow only in the 

 almost complete absence of oxygen (anaerobic species). Hence 

 the value of oxidising agents (e.g. peroxide of hydrogen) for the 

 cleansing of wounds, 



