CHAPTER I. 



Definition of bacteria Their place in nature Difference between 

 parasites and saprophytes Nutrition of bacteria Products of bac- 

 teria Their relation to oxygen Influence of temperature upon 

 their growth. 



BY the term bacteria is understood that large group 

 of minute vegetable organisms which multiply by a pro- 

 cess of transverse division. They are spherical, oval, 

 rod-like, and spiral in shape, and are commonly devoid 

 of chlorophyll. 1 Owing to the absence of chlorophyll 

 from their composition the bacteria are forced to either a 

 saprophytic 2 or parasitic 3 form of existence. 



Their life processes are so rapid and energetic that 

 they result in the most profound alterations in the 

 structure and composition of the materials upon which 

 they are developing. 



Decomposition and fermentation result from the pres- 

 ence of the saprophytic bacteria, while the changes 



1 Chlorophyll is the green coloring matter possessed by the higher 

 plants by means of which they are enabled in the presence of sun- 

 light to decompose carbonic acid (CO 2 ) and ammonia (XII,) into 

 their elementary constituents. 



* A saprophyte is an organism that obtains its nutrition from 

 dead organic matter. 



3 A parasite lives always at the expense of some other living, 

 organic creature, and in the strictest sense of the word cannot exist 

 upon dead matter. There exist, however, a group of so-called 

 "facultative" saprophytes and parasites which possess the power of 

 accommodating themselves to existing surroundings at one time 

 leading a parasitic, at another time a saprophytic form of existence. 



