PHYSIOLOGICAL LIGHT. 431 



The final result of the photogenic phenomenon is, then, a physico- 

 chemical one — physical as regards the emission of light, chemical as 

 regards the formation of a crystalline substance; but the formation 

 and transformations of the photogenic protoplasmic granulations are 

 the result of a physiological process and are the exclusive domain of 

 biological mechanics. 



77e may perhaps better comprehend the importance of the solution 

 of the problem of the mechanism of the photogenic function, a solution 

 which we have sought for many years, if we again read the words of 

 Claude Bernard, which are, as might be said, the scientific testament 

 of that illustrious physiologist, since they were those delivered by him 

 at the close of the last lecture which he gave at the Museum, on the 

 "Phenomena of life common to animals and vegetables," some time 

 before his death. 



" Arrived at the termination of our studies, we see that they lead us 

 to a very general conclusion, the result of experiment; namely, that 

 between the two schools, one holding that vital phenomena are abso- 

 lutely distinct from physico-chemical phenomena^ the other that they 

 are wholly identical with them, there is place for a third doctrine, 

 that of physical vitalism, which takes account of what there is peculiar 

 in the manifestations of life, and what there is that conforms to the 

 action of general forces; the ultimate element of the phenomenon is 

 physical, the arrangement is vital." ] 



The study of the photogenic function conducts us to physico-vitalism, 

 or, more exactly, to biological dynamics, which is a department, but a 

 special department, of general mechanics. 



1 Lemons sur les phe'noinfenes de la vie, Paris, 1879, p. 524. 



