n BACTERIA 257 



about j4,y mm. (jpnnr inch) in length. Like Sphaerella, 

 the Monad swims about by means of two flagella, but 

 it contains no chlorophyll. The putrefying infusion in 

 which it lives contains proteids in solution, in part split 

 up by the process of decomposition into simpler com- 

 pounds, some of which are diffusible. As the Monad 

 contains no chlorophyll, its nutrition is evidently not 

 holophytic ; and., apart from the fact that it possesses 

 neither mouth nor pseudopods, observation seems to 

 show pretty conclusively that it is not holozoic. 



There remains only one way in which nutrition can 

 take place, namely, by absorption of the proteids and 

 other nutrient substances in the solution : the Monad 

 may be said to live immersed in an immense cauldron of 

 broth which it is for ever imbibing, not by its mouth, for 

 it has none, but by the whole surface of its body. This 

 is the saprophytic mode of nutrition, and resembles that 

 which occurs in certain plants which contain no chloro- 

 phyll the fungi. It will be seen that the main differ- 

 ence between saprophytic and holozoic nutrition is that 

 in the former digestion, i.e., the process of rendering 

 food-stuffs soluble and diffusible takes place outside the 

 body, so that constructive metabolism can begin at once. 



In the Monad, the characters are again conflicting 

 (compare p. 255) : the probable absence of cellulose, the 

 presence of a contractile vacuole, and the flagella all 

 have an " animal " look, but the mode of nutrition is 

 that of a fungus. 



Decomposition, as already stated (p. 152), is due in 

 the first instance to the action of certain other minute 

 organisms, known as Bacteria, which appear in the 

 earlier stages of the putrefaction of an organic infusion. 

 The nutrition of these organisms, like that of Monads, 

 is usually saprophytic and the movements are generally 

 ciliary ; but as they have a definite cell -wall and no 



