
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.* 
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 (“ Comptes ren- 
dus of the Academy of Sciences,”’ 1870, vol. Ixxi., p. 372, and 1873, vol. 
Ixxvi., p. 352). 
