BACTERIA IN NATURE 9 



logy, classification and function of bacteria is called Bac- 

 teriology. 



Distribution of bacteria in nature. Bacteria exist 

 nearly everywhere in external nature. Their home is in the 

 soil, in water, in milk, on the skin of man and animals, and 

 on certain of their mucous membranes, especially those of 

 the alimentary tract. They are not usually found within the 

 tissues of healthy plants, or in the blood and tissues of 

 healthy animals, 1 and but rarely on certain of the mucous 

 membranes, such as those of the lungs, kidneys and bladder. 

 Occasionally they are carried through the skin or they pass 

 through the mucous membranes of the digestive tract after 

 which they may be found for a short time in the blood and 

 living tissues of the body. 2 



When considering the distribution of bacteria, it is 

 necessary to discriminate first of all between actively grow- 

 ing bacteria and latent forms. Highly resistant bacterial 

 spores, and the hardly less resistant dried vegetative forms 

 of some species, occur very generally upon the earth's sur- 

 face and upon the animals, plants, and inanimate objects 

 that cover it. They are, in short, ubiquitous. But living 

 bacteria in active growth or multiplication occur only where 

 the life conditions necessary for their multiplication are 



1 Ford (Transactions of the Asso. of Am. Physicians, Vol. XV 

 (1900) p. 389) found that at least 80% of the livers and kidneys of 

 healthy normal animals contain bacteria which will develop on 

 culture media if allowed to incubate for a sufficiently long time after 

 removal from the body. He states that other observers have obtained 

 negative results because they rejected their cultures too soon. Among 

 the bacteria isolated Ford obtained streptococci, M. pyogenes, Para- 

 colon, B. Mesentericus, vulgatus, fuscus, B. proteus, B. coli and 

 others. 



2 Nocard (Compt rendu de la Soc. de Biol., Vol. XLVII (1895) 

 found bacteria in the blood of horses when it was drawn at certain 

 times relative to feeding, but not at other times. Ravenel (Jour, of 

 Med. Research, Vol. X (1904) p. 460) verified previous observations 

 that the tubercle bacterium would pass through the mucous mem- 

 brane of the intestine when taken in connection with fat. 



