VITALITY OF PUTEEFACTIVE 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 sur la Bifere,' 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 farther 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. 



' Beitrage zur Biologic der Pflanzen, July 187G. 



' 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. With 

 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.' 



