ORIGI.V OF LOWEST ORGANISMS. 107 



faction is hindered by increased pressure and favoured 

 by diminution of pressure, may be placed under con- 

 ditions which are successively more favourable than 

 the last, by putting a gradually smaller and smaller 

 quantity of fluid into a flask, to which calcined air is 

 admitted, and, better still if the stimulus of oxygen 

 is not absolutely needed in order to incite fermenta- 

 tion in the fluid employed by only half filling the 

 flask, and procuring a more and more perfect vacuum. 

 In accordance with the doctrines of Baron Liebig, 

 therefore, my experiments, as well as those of many 

 other investigators, tend to show that fermentative and 

 putrefactive changes are merely processes of chemical 

 re-arrangement, which frequently take place as it 

 were " spontaneously ' - owing to the inherent insta- 

 bility of certain nitrogenous compounds in the presence 

 of free oxygen. My experiments have, however, also 

 revealed the additional fact that, under the combined 

 influence of heat and diminished pressure, some fluids 

 will undergo fermentation even in closed vessels, from 

 which all air has been expelled. They lend no sup- 

 port to the idea that the air is so thickly laden with 

 living germs as some would have us suppose ; and in 

 view of the mass of positive information now in our 

 possession concerning the degree of heat which suf- 

 fices to kill the lowest organisms, they also, as I think, 

 entitle us to come to the conclusion that such orga- 

 nisms are (as the microscopical evidence might lead us 



