268 GENERAL ANATOMY. 



that the smallest nervous vessels contain an aqueous fluid, serv- 

 ing for feeling, motion, and at the same time nutrition. 



The opinion of Mascagni as to the elementary composition 

 and nutrition of the parts, does not differ much from that of 

 Boerhaave. According to Mascagni, the division of the arte- 

 ries finishes at the point where, or having arrived at the tenui- 

 ty of a red globule of blood, they are converted into veins. 

 There, they are furnished with exhalent porosities, as well for 

 the secretions as for nutrition. In all parts there are orifices 

 of absorbent vessels for taking up and containing the nutritive 

 molecules. The elementary parts consist of absorbent vessels: 

 these, by their union, constitute the most simple membranes 

 and the smallest blood vessels, which form the most com- 

 pound membranes. 



In these two hypothesis, every thing is vascular, and nutri- 

 tion happens in the vessels; in the first, in the finest ramifica- 

 tions of the capillary arteries, in the second, in the finest radi- 

 cles of the absorbents. In both, the vessels constitute the mass 

 of the body, and are truly in a continual state of circulation. 



Bichat's opinion respecting the nutritious vessels and nutri- 

 tion, is somewhat different. According to this author, each 

 molecule of the organs is in a manner placed between two 

 patulous vessels; the one a nutritive exhalent which had de- 

 posited it, and the other a nutritive absorbent, destined to take 

 it up again. 



Prochaska, while he admits the direct communication be- 

 tween the arteries and veins, supposes that it is by the porosi- 

 ties of the parietes of the vessels and the general permeability 

 of the substance which forms the mass of the body, that nutri- 

 tion occurs. 



395. Nutrition, whatever may be its immediate channel, 

 presents a continual two fold motion of composition and de- 

 composition. The simplest animals directly inhale and exhale 

 the materials of this double phenomenon. Other animals, of 

 a more complex organization, have a tegument more or less 

 prolonged into the mass of the body, conveying there and 

 taking up again the matters which are added to it, and those 

 which are separated from it. Others, still more complex, have 



