12 TEXTBOOK OF BOTANY 



A living bacillus seems under a microscope even of the high- 

 est power to be merely a colorless body, two or three times as 

 long as wide, with rounded ends. If two or more cells are 

 attached, the ends by which they join one another are flat- 

 tened rather than rounded. 



Something more of the structure of the cell may be made out if it 

 is killed and stained by the use of suitable dyes. The process of stain- 

 ing is a delicate one and can be carried on successfully only after con- 

 siderable experience. A cell prepared in this way (Fig. 6, A) is seen 

 to be surrounded by a thin wall; within the wall is the protoplasm, 

 through which are scattered a few dark granules. Extending outward 

 from the wall are a number of long threads. These threads were part 

 of the living matter of the cell when it was alive, and it was by means 

 of the rapid vibration of the threads that the cell moved about in the 

 water. 



19. Food. This bacillus is commonly found in solutions 

 which, like the hay infusion, contain dead and more or less 

 decaying organic matter that is, matter which has been a 

 part of the bodies of plants or animals. From this fact we 

 may infer that the bacillus needs ready-made organic food 

 just as animals do, and this is the case. We shall see later 

 that green plants can build up their living matter out of very 

 simple materials ; but this is not true of bacteria. Many 

 bacteria live, like Bacillus subtilis, on the dead substances 

 of animals and plants. Bacteria and other plants which use 

 dead food are spoken of as saprophytes. Other bacteria, 

 which live upon or in the living tissues of plants or animals, 

 are parasites. 



20. How the Bacillus Obtains Food. The wall of the 

 bacillus cell is firm and rigid, and has no opening through 

 which food materials can be taken into the cell. Therefore 

 it is necessary that anything which the cell is to take in as 

 food must first be dissolved, since water and many substances 

 dissolved in water can pass through the cell wall. Such a 

 substance as the hay with which we started is, of course, not 

 soluble in water ; so the bacillus must change some or all of 



