MICROBES, OB BACTERIA. 117 



the aid of purely inorganic substances. Animals and 

 plants devoid of chlorophyl get their nutriment by 

 unmaking the complex substances elaborated by the 

 green parts of plants, and these act in the same way 

 for their own profit in those organs which have no 

 chlorophyl ; as, for instance, in the seed and embryo. 



IX. AEROBIES AND ANAEROBIES. 



We have seen that microbes, at different epochs 

 of their existence, and in accordance with the nature 

 of their environment, can assume very diverse forms. 

 Thus the organism, which at first appears in the form 

 of globules (micrococcus), either isolated or united in 

 more or less numerous colonies by a kind of muci- 

 laginous envelope (Zoogloea), when it again becomes 

 free, may be elongated in the shape of the figure 8, 

 which is formed of two cells about to separate; or 

 a large number may be included in the form of a 

 straight, articulated rod (Bacterium), or in a rod 

 which is curved, waved, or even spiral (Vibrio, 

 Spirillum, Spirochcete), always more or less mobile; 

 or, again, the cells may form long, stationary filaments 

 (Bacillus), etc. 



So also the habitat and mode of life divide the 

 microbes into very distinct classes. Some can only 

 ibsist when they breathe the natural oxygen they 

 ithdraw from the atmosphere; they can only exist 



