PUTREFACTION AND FERMENTATION 485 



of trees in the country, organisms formed in sixteen out of eighteen flasks, 

 and presented a great variet}^ in their nature.^ These experiments, which rest 

 not only on the high authority of M. Pasteur, but also on the unimpeachable 

 corroborative testimony of a Committee of the French Academy of Sciences, 

 including the celebrated Milne Edwards, prove conclusively both that the 

 gases of the air cannot of themselves occasion the growth of organisms, even 

 in a very favourable nidus for their development, and also that in regions 

 inhabited by plants or animals, whether in cities or in the country, nearh' 

 every cubic inch of atmosphere really does contain living germs floating in it. 

 But there is one other experiment related by Pasteur,'- which is in some 

 respects even more striking. A flask is prepared similar to those already 

 described, except that, after the introduction of the decoction of yeast, the 

 neck is not only drawn out into a pretty narrow tube, but bent at \'arious 

 angles. The fluid is then boiled as in the former experiments ; but the end 

 of the neck, instead of being sealed, is left open, so that air passes into the 

 flask on withdrawal of the lamp. The vessel being then left undisturbed, 

 the diurnal changes of temperature, involving alternate expansion by day 

 and condensation at night of the gases in the flask, necessitate a daily inter- 

 change between the air in the bod}^ of the flask and the external atmosphere. 

 Yet the fluid, though exposed in this way to air perpetuall}' changed, remains 

 for an indefinite period quite transparent, without trace of organic develop- 

 ment. There can be but one interpretation of this fact. The oxj^gen, whether 

 in its ordinary condition or that of ozone, with all the other atmospheric gases, 

 including any which may exist in such small quantities as to be undiscoverable 

 by the chemist, must pass, each in its own proportion, unchanged into the body 

 of the flask. It is impossible that a dry glass tube can stop any gas. For though 

 the tube is moist from condensation of aqueous vapour in the first instance, it 

 is soon dried by the air that passes in and out through it. It is, therefore, incon- 

 ceivable that any atmospheric gas can have been arrested by the tube. But 

 it is conceivable, considering the very gradual character of the movements of 

 the air in consequence of the diurnal changes, that dust, even though very fine, 

 may be arrested by the angles. We ma\', perhaps, wonder that particles of 

 such extreme minuteness as the germs of atmospheric organisms sliould be so 

 detained. But no one can say it is impossible, and no other possible explanation 

 presents itself. The experiment proves with certainty tliat the gases of the air, 

 however abundantly supplied, are of themselves unable to originate the growth 

 of torulae and the other minute organisms which appear in tlecoction of yeast 



' Sec Annates des Sciences Natinellcs, 1861 and 1805. 



' This experiment is attributed by Pasteur to M. Chevrcul. 



