276 



STRUCTURAL BOTANY 



wards cultivated by its discoverer in solutions of grape- 

 sugar, to which a little extract of meat had been added. 

 The formation of endospores characterises one great 

 group of Bacteria, and distinguishes them from similar 

 unicellular organisms. 



Bacillus suUilis, like most other living things, requires 



plenty of atmospheric 

 oxygen in order to flour- 

 ish. Some of the other 

 Bacteria, however, have 

 the remarkable peculiar- 

 ity that they thrive best 

 in the absence of free 

 oxygen. This is the case, 

 for example, with Bacillus 

 butyricus, the organism to 

 which the formation of 

 butyric acid by the fer- 

 mentation 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 ex- 

 periments have proved that light has a very unfavourable 

 effect on Bacteria, completely stopping their growth and 

 multiplication in many cases, and even/ when intense 

 enough, killing the cells outright. It is tjie rays towards 

 the violet end of the spectrum which exercise the 



Fiu. 110. Bacillus megatherium, a, 

 chain of vegetative rods, each con- 

 sisting of two or more cells, but 

 septa not shown. Magnified 250. 

 p, four-celled rod, after treatment 

 with alcoholic solution of iodine ; 

 b, vegetative rods ; c-f, successive 

 stages in formation of endospores ; 

 r, four-celled rod with ripe spores ; 

 9\~9s an( i ^i> ^s> spores swelling 

 before germination ; the mother cell- 

 walls disappear ; k-m, germination 

 of spores. All figures except a 

 magnified 600. (After De Bary.) 



