PUTEEFACTION AND INFECTION. 117 



all swarmiog with Bacterial life, five were green. They 

 were distributed as follows: — Beef 2, herring 1, had- 

 dock 1, fowl 1, wild duck 0. The same absence of 

 uniformity was manifested in the struggle for existence 

 between the Bacteria and the Penicillium. In some 

 tubes the former were triumphant; in other tubes of 

 the same infusion the latter was triumphant. It would 

 also seem that a want of uniformity as regards vital 

 vigour prevailed. With the self-same infusion the 

 motions of the Bacteria in some tubes were exceedingly 

 languid ; while in other tubes the motions resembled 

 a rain of projectiles, being so rapid and violent as to be 

 followed with difficulty by the eye. Reflecting on the 

 whole of this, I conclude that the germs float through 

 the atmosphere in groups or clouds, and that now and 

 then a cloud specifically different from the prevalent ones 

 is wafted through the air. The touching of a nutritive 

 fluid by a Bacterial cloud would naturally have a dif- 

 ferent effect from the touching of it by the sterile air 

 between two clouds. But, as in the case of a mottled 

 sky, the various portions of the landscape are succes- 

 sively visited by shade, so, in the long run, are the various 

 tubes of our tray touched by the Bacterial clouds, the 

 final fertilization or infection of them all being the 

 consequence.^ 



1 In hospital practice the opening of a wound during the pass- 

 age of a Bacterial cloud would have an effect very different from 

 the opening of it in the interspace between two clouds. Certain 

 caprices in the behaviour of dressed wounds may possibly be ac- 

 counted for in this way. 



Under the heading ' Nothing New under the Sun,' Professor 

 Huxley has lately sent me the following remarkable extract: — 

 * Uebrigens kann man sich die in der Atmosphare schwimmenden 

 Thierchen wie Wolken denken, mit denen ganz leere Luftmassen, 

 ja ganze Tage vollig reinen Luftverhaltnisse wechseln.' (Ehren- 

 berg, ' Infusionsthierchen,' 1838, p. 525.) The coincidence of 

 phraseology is surprising, for I knew nothing of Ehrenberg's con- 

 ception. My ' clouds,' however, are but small miniatures of his. 



