ORIGIN OF BACTERIA. 23 



CHAPTER II. 



ORIGIN OP BACTERIA AND THEIR DISTRIBUTION. 



As Pasteur has shown, all bacteria develop from pre-existing 

 bacteria, or the spores of the same. They cannot arise de novo. 



The wide and almost universal diffusion of bacteria is due to 

 the minuteness of the cells and the few requirements for their 

 existence. In. a drop of water 1700 million cocci can find room. 



Very few places are free from germs ; the air on the high seas, 

 and on the mountain tops, is said to be free from bacteria, 

 but it is questionable. 



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, ga-n-po^ putrid. <j>vr6v, 

 plant. Parasites, napd, aside of, ciToc, 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 Parasites. 



Conditions of Life and Growth of Bacteria. Influence of Tem- 

 perature. 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 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. 



