136 THE FLOATIXG-MATTEE OF THE AIR. 



by distilled water, and not rendered artificially acid, 

 neutral, or alkaline. I had occasion, however, to repeat 

 among others some of the very remarkable experiments 

 on supemeutralized hay-infusions described by Dr. 

 William Eoberts in his excellent paper in the Philo- 

 sophical Transactions for 1874. These experiments I 

 could not corroborate ; for while in his hands such 

 infusions sometimes required three hours' boiling to 

 sterilize them, in mine they behaved like other in- 

 fusions, and were sterilized in five minutes. 



In the abstract of the investigation communicated 

 to the Eoyal Society on the 13th of January, 1876, I 

 mentioned this discrepancy, and pointed out its possible 

 cause.' But the largeness of the question, which had 

 been long previously raised by M. Pasteur, and the 

 limitation of my time, led me to postpone it. This 

 postponement is mentioned at the conclusion of my 

 paper in the Philosophical Transactions for 1876, where 

 the discrepancy referred to is not at all discussed. 



In his celebrated paper, ' Sur les corpuscules orga- 

 nises qui existent dans 1' Atmosphere,' published fifteen 

 years ago,* M. Pasteur first announced that while acid 

 infusions had their germinal life destroyed by a tem- 

 perature of 100° C, a temperature over 100° was 

 needed to produce the same effect in alkaline infusions. 

 In his ' Etudes sur la Biere,' published in the early 

 part of 1876, he repeats and illustrates this statement. 

 Vinegar he finds has the organisms which decompose it 

 destroyed by a temperature of 50° C. Wine is ren- 

 dered unchangeable by a slightly higher temperature. 

 Beerwort without hops requires a temperature of 90° C. 

 to sterilize it, and milk a temperature of 110°. Fresh 

 urine has its organisms destroyed at a temperature of 



' Boy. Soc. Proo. vol. xxiv. p. 178. 

 « AnnaJes de Chimie, 1862, vol. Ixiv. 



