152 
PEOFESSOE TYNDALL ON THE DEPOETMENT AND VITAL 
Vinegar he finds has the organisms which decompose it destroyed by a temperature 
of 50° C. Wine is rendered unchangeable by a slightly higher temperature. Beer- 
wort without hops requires a temperature of 90° C. to sterilize it, and milk a tempera- 
ture of 110°. Fresh urine has its organisms destroyed at a temperature of 100°, while 
a higher temperature is needed when the urine has been neutralized by carbonate of 
lime * * * § . The resistance of alkalized urine to sterilization is therefore by no means a new 
announcement f. 
On my return from Switzerland last autumn the experiments on alkalized hay-infusions 
were resumed ; and soon afterwards Professor Cohn, of Breslau, so highly distinguished 
by his researches on Bacteria , placed in my hands a memoir J which rendered it doubly 
incumbent on me to examine more strictly the grounds of my dissidence from Dr. .Roberts. 
Professor Cohn is emphatic in his corroboration of Dr. Roberts §, having found, during a 
long and varied series of experiments with hay-infusions of divers kinds, that when the 
period of boiling did not exceed fifteen minutes organisms invariably appeared in the 
infusions afterwards. Sixty, eighty, and even one hundred and twenty minutes’ boiling 
were found in some cases insufficient to sterilize the infusions. One marked difference, 
however, exists between Dr. Roberts and Professor Cohn. The former found five 
minutes’ boiling sufficient to sterilize unneutralized hay-infusion, but one, two, and even 
three hours’ boiling insufficient to sterilize superneutralized hay-infusion ; while the 
latter noticed no difference of this kind, but found acid and neutral infusions equally 
resistant |j . 
* Etudes sur la Biere, p. 34. 
t With regard to the different action of acid and alkaline liquids, I put the subject purposely aside with the 
view to its full investigation as soon as the first instalment of these researches had been published. I could 
find no adequate explanation of the alleged fact that germs are killed in an acid liquid, while they survive in an 
alkaline one of the same temperature ; nor could the well -merited respect that I feel for M. Pasteub cause me 
to accept his explanation of the fact without further inquiry on my own account. In due time, therefore, I 
resolved to examine the question. Various experiments and explanatory views regarding it are recorded in the 
following pages. It is perhaps worth mentioning that in his communication to the Academy of Sciences Dr. 
Ba sti an so interprets my last paper (Phil. Trans. 1876, p. 57) as to make me say that which I had neither the 
warrant nor the wish to say — namely, that germs are killed in alkaline liquids of all kinds by one or two minutes’ 
exposure to a temperature of 212° F. 
t Beitrage zur Biologie der Pflanzen, July 1876. 
§ Professor Cohn gently censures me for taking exception to the cotton- wool plug, seeing that cotton-wool, 
even in my own experiments, has always proved a trustworthy filter. I did not, however, object to it as a 
filter, but on grounds which have in part, at all events, commended themselves to Professor Cohn himself. 
With reference to the method of Dr. Eobeexs he writes thus — ■“ The defect of this method consists in the difficulty 
of protecting the cotton-wool from accidental wetting by the infusion. The steam, moreover, which rises from 
the liquid penetrates the cotton-wool, and, through its partial condensation in the neck of the bulb, might 
readily charge itself with germs.” 
|| “Ein constanter Unterschied in der Zeitdauer zwischen sauren und neutralen Aufgiissen, wie ihn Eobeets 
gefunden, trat in unseren Versuchen nicht hervor” (p. 259). 
