VITALITY OF PUTREFACTIVE ORGANISMS. 137 



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.^ 



On my return from Switzerland in 1876 the experi- 

 ments 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 ^ which rendered it doubly incum- 

 bent on me to examine more strictly the grounds of my 

 dissidence from Dr. Eoberts. Professor Cohn is, on the 

 whole, emphatic in his corroboration of Dr. Eoberts,'^ 

 having found, during a long and varied series of ex- 

 periments with hay-infusions of divers kinds, that when 

 the period of boiling did not exceed fifteen minutes 

 organisms invariably appeared in the infusions after- 



* * Etudes siir la Bi^re,' p. 34. 



2 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. Pasteur cause me to accept 

 his explanation 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. 



^ Beitriige 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 experi- 

 ments, 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. Witli 

 reference to the method of Dr. Eoberts he writes thus : — < The de- 

 fect 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.' 



