180 Prof. J. Tyndall on the [Jan. 13, 



thickly inuddy, while spots of mould had formed on the majority of the 

 remaining tubes. Fifteen hours subsequent to this observation, viz. on 

 the morning of the 27th of October, all the tubes containing hay-infusion 

 were smitten, though in different degrees, some of them being much 

 more turbid than others. Of the turnip-tubes, three only remained un- 

 smitten, and two of these had mould upon their surfaces. Only one of 

 the thirty-five beef -infusions remained intact. A change of occupancy, 

 moreover, had occurred in the tube which first gave way. Its muddiness 

 remained grey for a day and a half, then it changed to bright yellow- 

 green, and it maintained this colour 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 resem- 

 blance to the propagation of a plague among a population, the attacks 

 being successive and of different degrees of virulence. 



From the irregular manner in which the tubes are infected we may 

 infer that, as regards quantity, the distribution of the germs in the air is 

 not uniform. 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 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 seem also as if a want of uniformity as regards 

 vital vigour prevailed. With the selfsame infusion the motions of the 

 Bacteria in some tubes were exceedingly languid, while in other tubes 

 they 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, 

 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 touching of it by the interspace between two 

 clouds. But as in the case of a mottled sky the various portions of the 

 landscape are successively visited by shade, so, in the long run, were the 

 various tubes of the tray touched by the Bacterial clouds, the final 

 fertilization or infection of them all being the consequence. The author 

 connects these results with the experiments of Pasteur on the non- 

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

 other experiments of his own *. 



* In hospital practice the opening of a wound during the passage of a Bacterial 

 cloud would have an effect very different from the opening of it in the interspace be- 

 tween two clouds. Certain caprices in the behaviour of dressed wounds may possibly 

 be accounted for in this way. 



Under the heading " Nothing new under the Sun," Prof. Huxley has just 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 



