286 



ON THE NUTRITION OF 



ly admissible with any other facts of secretion and 

 assimilation, in which we have chemical qualities 

 and effects which owe their existence to living 

 agency. 



A doctrine somewhat analogous may he extend- 

 ed to many substances, both animal and vegetable, 

 which are wholly immersed in fluids, of which we 

 have a good exemplification in the submarine tribe of 

 fuci. It is not incumbent on us to presume that, in 

 all such species, a mechanical propulsion of the nu- 

 tritious fluid must take place, similar to that which 

 obtains in the sanguiferous system of large animals, 

 or even to that which some scanty experiments are 

 considered as having substantiated in certain vege- 

 tables. The transmission may be conducted by so- 

 lution and precipitation alone. The motions may 

 be exactly similar to those in which a saline matter, 

 taken up from the concrete state at the bottom of a 

 liquid solvent, gradually ascends during solution, 

 while the liquid remains steady, its particles either 

 suffering no change of place, or such a change as we 

 may call chemical because it is strictly corpuscu- 

 lar, arising from chemical attraction and communi- 

 cation. It would be unphilosophical to say that 

 nutrition is nothing else than solution and precipi- 

 tation ; yet the local transmission of the nutriment 

 is sufficiently accounted for by this set of causes ; 

 and the mechanical propulsion of a body of fluid is 



