CHAPTER I. 



Deflaitiou of bacteria— Their place in nature— DiflFerence 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 the individual members 

 of which multiply by a process of transverse division. 

 They are spherical, oval, rod-like, and spiral in shape, 

 and are commonly devoid of chlorophyll.^ 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- or parasitic' form of existence. 



Their life-processes are so rapid, complex, and ener- 

 getic 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 saprophytic bacteria, while the 

 changes brought about in the tissues of their host by the 



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 (COj) and ammonia (NH3) into their elementary constit- 

 uents. 



- 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. 



