276 STRUCTURAL BOTANY 



the entire contents escape as an ordinary bacterial cell, 

 which at once begins to move about by means of cilia 

 (see Fig. 109, B). 



Fig. 110 shows very completely the stages in the forma- 

 tion and germination of the spores in another Bacillus, 

 called B. megatherium, because for one of the Bacteria it 

 is quite a monster, though its cells are only about Twth 

 of a millimetre in diameter. This species was originally 

 found in boiled cabbages, and was afterwards cultivated 

 by its discoverer in solutions of grape-sugar, to which a 

 little extract of meat had been added. The formation of 

 eudospores characterises one great group of Bacteria, and 

 distinguishes them from similar unicellular organisms. 



O l - J 



Bacillus suUilis, like most other living things, requires 

 plenty of atmospheric oxygen in order to nourish. Some 

 of the other Bacteria, however, have the remarkable 

 peculiarity that they thrive best in the absence of free 

 oxygen. This is the case, for example, with Bacillus luty- 

 ricus, the organism to which the formation of butyric acid 

 by the fermentation of sugar is due. In this case the 

 oxygen necessary for respiration is not absorbed in the 

 free state, but obtained from the breaking down of the 

 organic substance in which the organism lives. 



It may be mentioned here that numerous experiments 

 have proved that light has a very unfavourable effect on 

 Bacteria, completely stopping their growth and multi- 

 plication in many cases, and even, when intense enough, 

 killing the cells outright. It is the rays towards the 

 violet end of the spectrum which exercise the greatest 

 retarding effect on the growth of these creatures. The 

 action of light in checking the increase of these agents of 

 decomposition and disease is evidently a fact of great 

 practical importance. 



