696 THE POPULAR SCIENCE MONTHLY. 



ness remained gray for a day and a half, then it changed to bright 

 yellow green, and it maintained this color to the end. On the 27th 

 every tube of the hundred was smitten, the majority with uniform 

 turbidity ; some, however, with mould above and slime below, the 

 intermediate liquid being tolerably clear. The whole process bore a 

 striking resemblance to the propagation of a plague among a popula- 

 tion, the attacks being successive and of different degrees of virulence. 



From the irregular manner in which the tubes are attacked, we 

 may infer that, as regards quantity, the distribution of the germs in 

 the air is not vmiform. The singling out, moreover, of one tube of 

 the hundred by the particular bacteria that develop a green pigment 

 shows that, as regards quality, the distribution is not uniform. The 

 same absence of uniformity was manifested in the struggle for ex- 

 istence between the bacteria and penicillium. In some tubes the for- 

 mer were triumphant ; in other tubes of the same infusion the latter 

 were triumphant. It would seem also as if a want of uniformity as 

 regards vital vigor prevailed. With the self-same infusion the mo- 

 tions 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. Re- 

 flecting on the whole of this, the author concludes that the germs 

 float through the atmosphere in groups or clouds, with spaces more 

 sparsely filled between them. The touching of a nutritive fluid by a 

 bacterial cloud would naturally have a different effect from the touch- 

 ing of it by the interspace 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 in- 

 fection of them all being the consequence. The author connects 

 these views with the expei'iments of Pasteur on the non-continuity 

 of the cause of the so-called spontaneous generation, and with other 

 experiments of his own.' 



The tray of tubes proved so helpful in enabling him to realize 

 mentally the distribution of germs in the air, that on the 9th of No- 

 vember he exposed a second tray containing one hundred tubes filled 

 with an infusion of mutton. On the morning of the 11th, six of the 

 ten nearest the stove had given way to putrefaction. Three of the 

 row most distant from the stove had yielded, while here and there 

 over the tray particular tubes were singled out and smitten by the 

 infection. Of the whole tray of one hundred tubes twenty-seven 

 were either muddy or cloudy on the 11th. Thus, doubtless, in a con- 

 tagious atmosphere, are individuals successively struck down. On 



' In hospital practice, the opening of a wound during the passage of a bacterial 

 cloud would have an effect different from the opening of it in the interspace between 

 two clouds. Certain caprices in the behavior of wounds may possibly be accounted 

 for in this way. 



