6 A MANUAL OF BACTERIOLOGY 



smallest organised particle visible under the micro- 

 scope contains about two million molecules of 

 organic matter. 



The reproductive power of microbes is most 

 prolific; and Cohn has calculated that a single 

 microbe at the end of three days would have in- 

 creased to nearly forty-eight billions, a mass which 

 would weigh no less than 7500 tons. But this 

 astounding rate of reproduction is kept in check by 

 the limited supply of food, as well as by various 

 circumstances which make the environment unsuit- 

 able for such a rapid rate of increase. ' As a con- 

 sequence of their enormous fecundity, it will be 

 readily understood that they are ubiquitous. Every 

 surface teems with them; all natural waters are 

 infested by them ; even the skin of the most washed 

 of mankind ; even the moisture of the sweetest 

 mouth harbours them by the million ! One thing, 

 however, they cannot stand, and that is boiling. 

 Boil them or the stuff in which they are nourishing, 

 and they cease to live or, in other words, the liquid 

 or solid substance so treated is sterilised. By means 

 of sterilised nutriment we can test any object for 

 the presence of microbes or bacteria, as they are 

 sometimes called. We prepare a broth suitable for 

 their nourishment, and sterilise it. If kept her- 

 metically sealed (as are preserved vegetables and 

 tinned meats), no microbes will appear in the broth. 

 Touch the broth with any stick or stone, or add to 

 it a drop of purest spring water, and it will, after a 

 few hours, swarm with microbes and putrefy. This 

 was the discovery of Theodore Schwann, also cele- 



