48 THE FLOATING -MATTER OF THE AIR. 



lamp-glass, and b the black gap cut out of the beam 

 at its brightest point. The deeper portions of the 

 lungs were thus proved to be filled with optically 

 pure air, which, as such, had no power to generate the 

 organisms proved by Schwann to be essential to the 

 process of putrefaction.' 



It seemed that this simple method of examination 

 could not fail to be of use to workers in this field. They 

 had hitherto proceeded less by sight than by insight, 

 being in general unable to observe the physical character 

 of the medium in which their experiments were con- 

 ducted. But the method has not been much turned to 

 account ; and this year (1875) I thought it worth while 

 to devote some time myself to the more complete 

 demonstration of its utility. 



I also wished to free my mind, and if possible the 

 minds of others, from the uncertainty and confusion 

 which now beset the doctrine of ' spontaneous genera- 

 tion.' Pasteur has pronounced it ' a chimera,' and ex- 

 pressed the undoubting conviction that this being so it is 

 possible to remove all parasitic diseases from the earth. 

 To the medical profession, therefore, and through them 

 to humanity at large, this question, if the illustrious 

 French pliilosopher be correct, is one of the last import- 

 ance. But Pasteur's labours, which have so long been 

 considered models by most of us, have been subjected to 



' 'No putrefaction,' says Cohn, 'can occur in a nitrogenous sub- 

 stance if it be kept free from the entrance of new Bacteoda after 

 those wliich it may contain have been destroj'ed. Putrefaction 

 begins as soon as Bactena, even in the smallest numbers, are acci- 

 dentally or purposely introduced. It progresses in direct proportion 

 to the muHi]>lication of the Bacteria; it is retarded when the Bac- 

 teria (for example, by a low temperature) develop a small amount 

 of vitality, and is brought to an end by all inlluences which either 

 stop the development of the Bacteria, or kill them. All bacteri- 

 cidal media arc tlierefore antiseptic and disinfecting.' — Beitrdge 

 zu/r Biologic (Icr Pjlanzeii, zweites Heft, 1872, p. 203, 



