8 Mr. Faraday on 



In order to understand Pasteur's general idea it is 

 necessary to 'follow the sequence of his researches. A 

 student under Delafosse and Dumas, Pasteur plunged en- 

 thusiastically into the study of crystallography, at the time 

 when Mitscherlich communicated to the Paris Academy of 

 Sciences his discovery that two otherwise identical solu- 

 tions, the tartrate and paratartrate of ammonia, had this 

 difference, that the former rotated the plane of polarised 

 light, while the latter, in this respect, was inert. Pasteur 

 found that the apparently inert solution was really a com- 

 pound of two acids, one of which rotated to the right and 

 the other to the left, the opposing influences being neutralised 

 in combination. Having been led to the discovery by ob- 

 serving the dissymmetry of the crystals, Pasteur inferred 

 that the molecules of the solution are also built up on a 

 dissymmetrical plan, and proceeding to examine a great 

 variety of substances, he arrived at the conclusion that only 

 those compounds which are the derivatives of life possess 

 this molecular dissymmetry. In other words life alone, 

 acting on matter, builds up dissymmetrical molecules, and 

 of this molecular dissymmetry, the rotation of the plane of 

 polarised light is the visible evidence. 



In his endeavour to explain Pasteur's views, Dr. Tyndall 

 states that in Pasteur's mind the agents of vitality are dis- 

 symmetric forces. It may be doubted whether this bare 

 statement, though based on a passage in M. Radot's book, 

 fully expresses Pasteur's idea. I believe that Pasteur would 

 equally accept the statement that the ordinary or sym- 

 metrical forces of matter, acting under the control of the 

 condition or agency called life, become dissymmetrical and 

 result in dissymmetry. Pasteur seems to have an idea of a 

 dissymmetrical influence which controls the ensonble of the 

 universe, of which ensemble the " straight-line " forces of Dr. 

 Tyndall are as much the elements as the substances we 

 know as matter. Pasteur sees this influence expressed in 



