314 Professor Tyndall on Oerms. 



is understood by this term in medicine. Toward the end of the 

 period of latency, the fall into a state of disease is comparatively 

 sudden ; the infusion passing from perfect clearness to cloudiness 

 more or less dense in a few hours. 



Thus the tube placed in Mr. Darwin's possession was clear at 

 8.30 A. M. on Oct. 19, and cloudy at 4.30 p. m. Seven hours, more- 

 over, after the first record of our tray of tubes, a marked change 

 had occurred. It may be thus desenbed : — Instead of one, eight 

 of the tubes containing hay-infusion had fallen into uniform inud- 

 diness. Twenty of these had produced Bacterial slime, which had 

 fallen to the bottom, every tube containing the slime being 

 covered by mould. Three tubes only remained clear, but with 

 mould upon their surfaces. The muddy turnip-tubes had increased 

 from four to ten ; seven tubes were clouded, while eighteen of 

 them remained clear, with here and there a speck of mould on the 

 surface. Of the beef, six were cloudy and one thickly muddy, 

 while spots of mould had formed on the majority of the remaining 

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

 morning of Oct. 27, 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 

 unsmitten, 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 gray for a day and a half, then it 

 changed to bright yelloAV 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 striking resemblance to the propa- 

 gation 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 attacked, 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 ))etween the Bacteria and the penicU- 

 lium. 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 vigor 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 ditticulty 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 eft'ect from the touching ot 



