CHAPTER I. 



Definition of bacteria Differences between parasites and saprophytes 

 Their place in nature Bacterial enzymes Products of bacteria 

 Nutrition of bacteria Their relation to oxygen Influence of 

 temperature upon their growth Chemotaxis. 



BACTERIA (more properly bacteriacese or schizomy- 

 cetesj were regarded by the older writers as infusoria. 

 This was because of their capacity for developing in 

 infusions, their property of spore-formation, their resist- 

 ance to drying, their power of independent motion, and 

 the absence of chlorophyll from their tissues. In the 

 modern conception, however, this classification is unten- 

 able, and bacteria, by virtue of their distinguishing 

 peculiarities, are now treated as a group by themselves 

 that may briefly be defined as comprising microscopic, 

 unicellular, vegetable organisms that multiply by the 

 process of transverse division. 



Inasmuch as bacteria are not possessed of chloro- 

 phyll, 1 their metabolic processes are fundamentally dif- 

 ferent from those of the higher plants in which it is 

 present. They cannot, as in the case of the green 

 plants, obtain carbon and nitrogen from such simple 

 bodies as carbon dioxide and ammonia, but are forced 

 to secure these essential elements from organic matter 

 as such. This power to decompose and assimilate 



1 Chlorophyll is the green coloring-matter possessed by the higher 

 plants by means of which they are enabled in the presence of sunlight 

 to decompose carbonic acid (COa) and ammonia (NHs) into their ele- 

 mentary constituents. 



31 



