384 lioyal Society : — 



the support and active multiplication of any such organisms as 

 may have been purposely added to them. Amongst such fluids I 

 may name that now commonly known as " Pasteur's solution," and 

 also one which I have myself more commonly used, consisting of 

 a simple aqueous solution of neutral ammonic tartrate and neutral 

 sodic sulphate*. AYhen portions of either of these fluids are 

 boiled and poured into superheated flasks, they \\tX\ continue quite 

 clear for many days, or even for weeks ; that is to say, although 

 the short and rather narrow neck of the flask remains open the 

 fluids will not become turbid, and no Bacteria are to be discovered 

 when they are submitted to microscopical examination. 



But in order to show that such fluids are still thoroughly 

 favourable media for the multiplication of Bacteria, all that is 

 necessary is to bring either of them into contact with a glass rod 

 previously dipped into a fluid containing such organisms. In about 

 thirty-six hours after this has been done (the temperature being 

 about 80° F.), the fluid, which had hitherto remained clear, becomes 

 quite turbid, and is found, on examination with the microscope, to 

 be swarming with Bacteria'^. 



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

 Sanderson + to hold good for portions of boiled "Pasteur's solu- 

 tion." 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 justify- 

 ing 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 

 atmosphere having thus been got rid of and shown to be delusive, 

 I am now able to bring forward other evidence tending to show 

 that the first Bacteria which appear in many boiled infusions 

 (when they subsequently undergo putrefactive changes) are evolved 

 de novo in the fluids themselves. These experiments are more- 

 over so simple, and may be so easily repeated, that the e\'idence 

 which they are capable of supplying hes within the reach of all. 



That boiling the experimental fluid destroys the life of any 

 Bacteria or Bacteria-gevm.s preexisting therein is now almost uni- 

 versally 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 wiU 

 continue (if left in the same flask) clear for an indefinite period ; 

 whilst a similarly infected portion of the same fluid, not subse- 

 quently 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 



* In the proportion of 10 grains of the former and 3 of the latter to 1 ounce 

 of distilled water. 



t The Modes of Origin of the Lowest Organisms, 1871, pp. 30, 51. 



t Thirteenth Report of the Medical Officer of the Privv Council (1871), 

 p. 59. 



