ORIGIN OF BACTERIA AND THEIR DISTRIBUTION 23 



One kind of bacterium will not produce another kind. A 

 bacillus does not arise from a micrococcus, or the typhoid fever 

 bacillus produce the bacillus of tetanus. 



This subject has been long and well discussed, and it would 

 take many pages to state the "pros" and "cons"; therefore this 

 positive statement is made, it being the position now held by 

 the principal authorities. 



Saprophytes and Parasites (Saprophytes: <ra^o?, putrid; 

 <f>!>Toy, plant. Parasites: xapd, aside of; <T~ITOS, food). 

 Those bacteria which live on the dead remains of organic life 

 are known as saprophytic bacteria, and those which choose the 

 living bodies of their fellow-creatures for their habitat are called 

 parasitic bacteria. Some, however, develop equally well as 

 saprophytes and parasites. They are called facultative para- 

 sites. 



Conditions of Life and Growth of Bacteria. Influence 

 of Temperature. In general, a temperature ranging from 10 

 C. to 40 C. is necessary to their life and growth. 



Saprophytes take the lower temperatures; parasites, the tem- 

 perature more nearly approaching the animal heat of the warm 

 blooded. Some forms require a nearly constant heat, growing 

 within very small limits, as the bacillus of tuberculosis. 



Some forms can be arrested in their development by a warmer 

 or colder temperature, and then restored to activity by a return 

 to the natural heat. 



A few varieties exist only at freezing-point of water, and 

 others again will not live under a temperature of 60 C. 



For the majority of bacteria a temperature of 60 C. is 

 destructive; and several times freezing and thawing very fatal. 



Influence of Oxygen. Two varieties of bacteria in relation 

 to oxygen the one aerobic, growing in air; the other, anae- 

 robic, living without air. 



Obligate aerobins, those which exist only when oxygen is 

 present. 



Facultative aerobins, those that live best when oxygen is 

 present, but can live without it. 



Obligate or true anaerobins, those which cannot exist where 



