204 PRACTICAL BACTERIOLOGY. 



Under favourable circumsfcances, especially if the 

 temperature is sufficiently high, spores are formed. 

 These are elliptical in form, do not lie exactly in the 

 centre of the cell, and are very resistant. Generally 

 the cells are distinctly swollen in the middle. If once 

 the spores are allowed to become fully mature, con- 

 trast staining is no longer very successful, as the rod- 

 lets themselves no longer become distinctly coloured. 



A third very interesting anaerobe is the Tetanus 

 bacillus. Tetanus, one of the most terrible of diseases, 

 occurs in man, and almost without exception ends 

 fatally. It has been observed that this illness occurs 

 most frequently as a consequence of wounds to which 

 earth, especially such as contains decomposing organic 

 matter, has come into contact, even if the injury were 

 only an imperceptible tearing of the skiu, or a mere 

 scratch. In such wounds a delicate slender bacillus, 

 at one end of which there is frequently a spore, has 

 been found. This spore is much thicker than the 

 bacillus itself, and thus causes a great swelling in it, 

 so that a peculiar drum-stick appearance is produced, 

 which is very characteristic. 



The Tetanus bacillus can only be cultivated if the 

 air is completely excluded ; it is quite as sensitive to 

 the presence of oxygen as the two preceding bacteria. 

 It develops best at blood heat, but growth is not 

 arrested, although it is not so rapid, if the prepara- 

 tions are kept at ordinary room temperatures. In 



