ORIGIN OF BACTERIA. 25 



he named ptomaines, from rttupa (corpse), because obtained 

 from putrefying objects. 



Fermentation. This form of "splitting up" fermentation, 

 as it is called is due to the direct action of vegetable organisms. 

 Many bacteria have the power of ferments. 



Putrefaction. When fermentation is accompanied by devel- 

 opment of offensive gases, a decomposition occurs, which is 

 called putrefaction, and this, in organic substances, is due 

 entirely to bacteria. 



Liquefaction of Solid Gelatine. Some varieties of bacteria 

 digest the nutrient gelatine, and so dissolve it ; others excrete 

 a ferment which liquefies the gelatine. 



Producers of Disease. Various pathological processes are 

 caused by bacteria, the name given to such diseases being 

 infectious diseases and the germs themselves called disease-pro- 

 ducing pathogenic bacteria. Those which do not form any 

 pathological process are called non-pathogenic bacteria. 



Pigmentation. Some bacteria are endowed with the property 

 of forming pigments either in themselves, or producing a chro- 

 mogenic body which, when set free, gives rise to the pigment. 

 In some cases the pigments have been isolated and many of the 

 properties of the aniline dyes discovered in them. 



Phosphorescence. Many bacteria have the power to form 

 light, giving to various objects which they inhabit a character- 

 istic glow or phosphorescence. 



Fluorescence. An iridescence, or play of colors, develops in 

 some of the bacterial cultures. 



Gas Formation. Many bacteria, anaerobic ones especially, 

 produce gases, noxious and odorless ; in the culture-media the 

 bubbles which arise soon displace the media. 



Odors. Some germs form odors characteristic of them : some 

 sweet, aromatic ones, and others very foul, disagreeable smells ; 

 some give a sour or rancid exhalation. 



Effect of Age. With age, bacteria lose their strength and die. 



Bacteria thus carry on all the functions of higher organized 

 life ; they breathe, eat, digest, excrete, and multiply ; and they 

 are very busy workers. 



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