254 NATURE AND LIFE. 



any case, investigations of this kind have a very great in- 

 terest. They give us the means of determining the rela- 

 tions between the molecular weights of immediate princi- 

 ples, and their nutritive coefficients. On the other hand, 

 by introducing at a given time a certain assimilable prin- 

 ciple into the organism, and marking the time that elapses 

 between the moment of its entrance and that of its issue, 

 we have a process for measuring the speed of nutritive 

 movement. 1 



We do not dwell any longer on these experiments. It 

 is enough for us to have traced succinctly their general 

 direction in agreement with the movement going on in the 

 rest of physiology. No doubt, such labors are tedious and 

 difficult. Besides knowledge and patience, we need, to 

 attack them, faith and imagination ; but the labors of the 

 present can only be fruitful on the condition of a clear vi- 

 sion of ideal truth, that glorious star in which the philoso- 

 pher deserving that name will never cease with passionate 

 striving to read the destinies of the spirit. 



1 See two memoirs published by me on this subject (" Gomptes ren- 

 dus of the Academy of Sciences," 1870, vol. Ixxi., p. 372, and 1873, vol. 

 Ixxvi., p. 362). 



