Spontaneous Generation 5 



the air through molten metal; and Schroder and Dusck 

 simplified the matter still further, in 1854, by demon- 

 strating that the air could be deprived of its micro- 

 organisms by being passed through a cotton plug. 

 Hoffmann, and, likewise, Pasteur, went a step further, 

 and proved that even the cotton filter was unnecessary 

 for making the air incapable of setting up putrefaction 

 in sterile meat broth. By drawing out the neck of the 

 flask into a long, capillary tube, and by bending the 

 latter, the dust particles in the air, and, among them, 

 the bacteria, were made to settle out before they reached 

 the liquid, and no putrefaction occurred in the latter. 



Another proof of the falsity of the idea of sponta- 

 neous generation was given by Tyndall, when he demon- 

 strated that perishable articles did not spoil on the tops 

 of high mountains, due to the fact that the air in those 

 altitudes contained no germs. 



The belief in spontaneous generation was gradually 

 shown to be untenable. Certain proof was supplied 

 that no putrefaction and decay take place in the 

 absence of bacteria. The occasional failure to secure 

 complete sterilization by boihng was accounted for 

 by Kohn's discovery in 1875, of spores, — certain rest- 

 ing stages in the growth of bacteria, more resistant 

 to heat than the vegetative cells, and capable of with- 

 standing boiling temperatures for some time. 



The physiology of bacteria. — Pasteur's epoch-making 

 investigations on fermentation shed a broader light 

 on the activities of microorganisms. His work plainly 

 indicated that various kinds of bacteria possess 

 specific functions and differ in the chemical changes 



