198 PKOGEESS OF MICROSCOPICAL SCIENCE. 



experimental fluids. This conclusion I believe to be erroneous, be- 

 cause in the former series of experiments which I performed in his 

 presence, and of which he recorded the results in your pages,* fer- 

 mentation occuiTed in the majority of cases in fluids which I have 

 very good reasons for believing to have been raised to a temperature 

 of 103"* 33 Ct The method recently employed by Dr. Sanderson for 

 superheating his flasks was needlessly complicated, and the exact 

 temperature to which they had been exposed was known only by 

 inference — never by direct thermometric observation. 



Leaving now the discussion of the experimental facts, I come to 

 the examination of Dr. Sanderson's inferences, which seem still more 

 open to objection. 



Dr. Sanderson, in common with most others, had up to the date of 

 his witnessing my experiments, admitted that bacteria and theii- genns 

 were killed in all fluids with which he had exj)erimented at the 

 temi:)erature of 100^ C. J It was, indeed, this conviction which 

 inspired himself, and many others, with a strong disbelief in the 

 results which I obtained with previously boiled infusions. 



What remains, then, for Dr. Sanderson to do, prior to divawing 

 inferences such as he now expresses, is to ascertain, by direct ex- 

 amination, whether the temperature of 100° C. is or is not fatal to the 

 life of bacteria. It is upon this that the interjiretation of my results 

 can alone dej^end. I have already contributed my share to the 

 inquiry by several long series of experiments, each of which has led 

 me to the same conclusion, viz. that bacteria and their germs, when 

 in the moist state, are killed at a temperature of 60^ C. § It is for 

 Dr. Sanderson, or any competent observers who are suificiently in- 

 terested, to examine my experiments and results on this j^art of the 

 subject, or else to devise others for themselves having a similar 

 bearing. 



If I am right in believing that 60° C. is the thermal death-point 

 of bacteria in the moist state, the conclusion which must be drawn 



* ' Nature,' vol. vii., p. 180. 



t Dr. Sanderson was not aware of this fact, and sa3's he does not know any 

 means by which the temiDCrature of a iluid boiling briskly in a vessul from which 

 the steam escapes only through a capillary orifice, could be accurately estimated. 

 The method wljich I adopted some months ago seems to possess this merit. I had 

 a small maximum thermometer made for the purpose, 2J in. in length, and 

 graduated from 95"-115^ C. Having straightened the neck of one of my retorts 

 (capable of holding about two fluid ounces), it was filled with some hay infusion 

 and the thermometer was introduced in sucli a way that its bulb remained in flie 

 midst of the fluid, about three-quarters of an incli away from the glass. The 

 long neck of the retort having then been drawn out and broken off (so as to leave 

 the usual capillary orifice), the fluid was boiled for five minutes before the vessel 

 was sealed. The thermometer was found to stand at 103° 'oS C. The retorts 

 employed in my previous experiments with Dr. Sanderson were of the same size, 

 and their contained fluids were boiled under precisely similar conditions. If 

 larger flasks, containing more fluid, were employed, the temperature would 

 doubtless rise to a still higher degree owing to a corresponding increase in 

 internal pressure. 



t See ' Thirteenth Keport of Medical Officer of Privy Council, 1871.' 



§ See ' Beginnings of Life,' vol. i., pp. 325-333 ; ' Proceedings of Royal Society,' 

 No. 143, 1873; and another paper about to appear in the next number of the 

 ' Proceedings.' 



