CHAPTER I. 



Definition of bacteria Their place in nature Difference between parasites 

 and saprophytes Nutrition of bacteria Products of bacteria Their relation 

 to oxygen Influence of temperature upon their growth. 



BY the term bacteria is understood that large group 

 of minute vegetable organisms which multiplies by a 

 process 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 obtain 

 their nutritive materials from organic matters as such, 

 and lead, therefore, 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 in and upon 

 which they are developing. 



Decomposition, putrefaction, and fermentation result 

 from the activities of the saprophytio bacteria, while 

 the changes brought about in the tissues of their host 



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 decom- 

 pose carbonic acid (CO 2 ) and ammonia (NH 3 ) into their elementary con- 

 stituents. 



2 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 crea- 

 ture, known as its host, and in the strictest sense of the word cannot develop 

 upon dead matter. There is, however, a group of so-called "facultative" 

 saprophytes and parasites which possess the power of accommodating them- 

 selves to existing surroundings at one time leading a parasitic, at another 

 time a saprophytic form of existence. 



