[26] M. Pasteur attempted to make a distinction in the case of slightly alkaline or neutral fluids (loc. cit., pp. 60–65). I have endeavoured to show the untenability of his conclusion in ‘Nature,’ 1870, No. 37, pp. 224–227. _Limits of ‘Vital Resistance’ to Heat displayed by Bacteria and Torulæ._ After stating elsewhere[27], that _Vibriones_ are partly broken up or disintegrated by an exposure for a few minutes to a temperature of 212° F. in an infusion which is being boiled, and also that, in all probability, the life of _Bacteria_ would be destroyed by such a treatment, I made the following remarks:--“With reference to these organisms, however, one caution is necessary to be borne in mind by the experimenter. The movements of monads and Bacteria may be, and frequently are, of two kinds. The one variety does not differ in the least from the mere molecular or Brownian movement, which may be witnessed in similarly minute, not-living particles immersed in fluids. Whilst the other seems to be purely vital--that is, dependent upon their properties as living things. These vital movements are altogether different from the mere dancing oscillations which not-living particles display, as may be seen when the monad or Bacterium darts about over comparatively large areas, so as frequently to disappear from the field. After an infusion has been exposed for a second or two to the boiling temperature, these vital movements no longer occur, though almost all the monads and Bacteria may be seen to display the Brownian movement in a well-marked degree. They seem to be reduced by the shortest exposure to a temperature of 100° C. to the condition of mere not-living particles, and then they become subjected to the unimpaired influence of the physical conditions which determine these movements.” I now have various facts to add in confirmation of these conclusions, and in extension of our knowledge concerning the vital resistance to heat of _Bacteria_ and _Torulæ_. [27] ‘Nature,’ 1870, No. 35, p. 171.