PROGRESS OF MICROSCOPICAL SCIENCE. 231 



and is found, on examination with the microscope, to be swarming 

 with Bacteria* 



" Facts of the same kind have also been shown by Dr. Burdon 

 Sanderson f to hold good for portions of boiled ' Pasteur's solution.' 

 Air was even drawn through such a fluid daily for a time, and yet it 

 continued free from Bacteria. 



" Evidence of this kind has already been widely accepted as justi- 

 fying the conclusion that living Bacteria or their germs are either 

 wholly absent from, or, at most, only very sparingly distributed 

 through, the atmosphere. The danger of infection from the atmo- 

 sphere having thus been got rid of, and shown to be dehtsive, I am 

 now able to bring forward other evidence tending to show that the 

 first Bacteria which appear in many boiled infusions (when they sub- 

 sequently undergo putrefactive changes), are evolved cle novo in the 

 fluids themselves. These experiments are, moreover, so simple, and 

 may be so easily repeated, that the evidence which they are capable 

 of supplying lies within the reach of all. 



" That boiling the experimental fluid destroys the life of any Bac- 

 teria or Bacteria-germs pre-existing therein is now almost universally 

 admitted ; it may, moreover, be easily demonstrated. If a portion 

 of ' Pasteur's solution ' be purposely infected with living Bacteria, 

 and subsequently boiled for two or three minutes, it will continue (if 

 left in the same flask) clear for an indefinite period ; whilst a similarly 

 infected portion of the same fluid, not subsequently boiled, will rapidly 

 become turbid. Precisely similar phenomena occur when we operate 

 with the neutral fluid which I have previously mentioned ; and yet 

 M. Pasteur has ventured to assert that the germs of Bacteria are not 

 destroyed in neutral or slightly alkaline fluids which have been 

 merely raised to the boiling-point. J 



" Even M. Pasteur, however, admits that the germs of Bacteria and 

 other allied organisms are killed in slightly acid fluids which have 

 been boiled for a few minutes ; so that there is a perfect unanimity of 

 opinion (amongst those best qualified to judge) as to the destructive 

 effects of a heat of 212° F. upon any Bacteria or Bacteria-germs 

 which such fluids may contain. 



"Taking such a fluid, therefore, in the form of a' strong filtered 

 infusion of turnip, we may place it after ebullition in a superheated 

 flask with the assurance that it contains no living organisms. Having 

 ascertained also by our previous experiments with the boiled saline 

 fluids that there is no danger of infection by Bacteria from the atmo- 

 sphere, we may leave the rather narrow mouth of the flask open, as 

 we did in these experiments. But when this is done, the previously 

 clear turnip-infusion invariably becomes turbid in one or two days 

 (the temperature being about 70° F.), owing to the presence of 

 myriads of Bacteria. 



" Thus if we take two similar flasks, one of which contains a boiled 



* The ' Modes of Origin of Lowest Organisms,' 1871, pp. 30, 51. 

 t Thirteenth Eeport of the Medical Officer of the Privy Council (1S71), p. 59. 

 % How unwarrantable such a conclusion appears to be, I have elsewhere endea- 

 voured to show. See ' Beginnings of Life,' 1872, vol. i. pp. 326-333, 372-399. 



VOL. IX. S 



