CHAPTER V 



DISTRIBUTION AND ORIGIN 



Distribution of Bacteria ; Their modes of life ; 

 Spontaneous Generation. 



It would be impossible to give a more concise and, at the same time, 

 accurate account of the distribution of bacteria in nature than is furnished 

 by Goethe's lines in ' Faust ' : 



' Der Luft, dem Wasser wie der Erden 

 Entwinden tausend Keime sich 

 Im Trocknen, Feuchten, Warmen, Kalten ! ' 



While Mephisto's haughty words : 



' Hatt' ich mir nicht die Flamme vorbehalten ; 

 Ich hatte nichts Apart's fur mich' 



remind us that fire is the most powerful weapon that mankind possesses 

 against bacteria. Unfortunately it is an engine of destruction that cannot 

 always be employed. 



In discussing the question of distribution, it is necessary to discriminate 

 first of all between actively growing bacteria and latent germs. Highly 

 resistant bacterial spores, and the hardly less resistant dried vegetative cells 

 of many species, occur everywhere upon the earth's surface and upon the 

 animals, plants, and inanimate objects that cover it. They are, in short, 

 ubiquitous. But living bacteria in active growth and multiplication only 

 occur where certain conditions necessary to their welfare are fitlfilled ; above 

 all, presence of water — the vital element of all organisms — a suitable tem- 

 perature and a suitable supply of food. In nature such conditions are found 

 in ponds or rivers contaminated by dead plants or animals, in dung, manure, 

 and moist soil. In our dwellings it is chiefly in milk and other dairy 

 produce, stale meat, and victuals of all kinds that bacteria are found. The 

 majority of them, both in and out of doors, belong to harmless species, but 

 there is no doubt that occasionally pathogenic forms occur. To find out 

 the natural haunts of these dangerous neighbours, places where they are 



