.Appendix. 



zymotic changes (putrefaction) with the presence of such parti- 

 cles. The experiments show that there are particles of matter 

 in the air which are ultra-microscopic in size, and yet their 

 presence can be made evident by their power of refracting light, 

 and secondly, whenever air depiived of such particles is brought 

 in contact with putrescible solutions no putrefaction occurs, but 

 that it invariably occurs wherever the air does contain such par- 

 ticles. An air tight box with a glass side and windows in the 

 ends had sealed to its bottom twelve test tubes with their mouths 

 upward and projecting inside the box. In the top was an India 

 rubber stuffing box through which passed a glass tube by means 

 of which infusions could be dropped into the test tubes. The 

 whole interior was smeared with glycerine and the apparatus 

 allowed to stand a number of days. By subsidence, then, all 

 foreign matter was caught and retained on the bottom. Now 

 when the electric beam is passed through the box, the space 

 inside appears perfectly dark, and the freedom from dust is thus 

 proven, for, so long as there are floating particles, the -track of 

 the beam can be detected. Then organic solutions of different 

 sorts were dropped into the tubes and boiled from below (the 

 tubes being made to project from the bottom of the box, for this 

 purpose; for a space only of five minutes. In no single instance, 

 except where the cause of the failure was obvious, did any turbid- 

 ity occur in the solution, nor was organic life (bacteria) found 

 after even a lapse of weeks and of months. The conclusion thus 

 reached by Prof. Tyndall is that the power of scattering light 

 and of developing bacterial life by the atmosphere go hand in 

 hand, and both are dependent upon the presence of particles 

 which, even by the highest powers of the microscepe, we cannot 

 detect. As bacterial life is regarded as necessary to putrefaction, 

 incidentally, therefore, spontaneous generation is held to be neg- 

 atived by these experiments. This deduction will be accepted or 

 rejected according as one is inclined to side with one or the other 

 parties to the controversy. I cannot refrain from expressing my 

 own opinion, that not only are the experiments of the utmost 

 exactness, but also that already they have led to results which 

 will contribute very materially to the ultimate solution of this 

 problem. 



