268 DIGESTION. 



disposed to be absorbed through the veins, are precisely those 

 which Graham found relatively little capable of diffusion, as, for 

 instance, albumen, and in part also, sugar. 



Considering the near relation in which the volatility of these 

 substances undoubtedly stands to their diffusibility, we can hardly 

 wonder that there should be so many volatile matters in the class 

 of easily resorbable bodies. The third and fourtli groups of these 

 transudable substances especially belong to this class ; but there 

 is no group in which we more distinctly perceive the dependence 

 of resorbability upon these physical properties than in the second 

 one ; for Graham's experiments on diffusion, as well as the 

 numerous endosmotic experiments which have been made with 

 the acids, explain their easy transition into the capillaries. If we 

 could suppose that the diffusibility and similar properties of a 

 substance were alone dependent upon certain fundamental pro- 

 perties pertaining to it, we should find a certain simplicity in the 

 form of composition of most of the above groups. These sub- 

 stances have either a mere binary composition, or, at all events, 

 like the haloid bases and alkaloids, they have, according to the 

 most recent chemical investigations, a very simple constitution, 

 approximating to the binary law ; while such soluble matters as do 

 not belong to the above groups, as albumen, emulsin, gum, and 

 even sugar, have hitherto baffled all the efforts of chemists to 

 comprehend their composition in accordance with the ordinary 

 views of chemical affinity or polarity. 



Although we have endeavoured in the above remarks to 

 consider from purely physical points of view the absorbing 

 capacity of the capillaries and the capability of certain substances 

 to be absorbed by them, we hope that our feeble attempt will not 

 be so far misconceived as to leave the impression that we would 

 wish to characterise the process operating in the animal body as 

 actually physical in its nature. We are, on the contrary, far from 

 entertaining such an opinion ; for the physical facts presented to 

 our notice do not, in our opinion, present sufficiently strong 

 indications to enable us to establish with completeness any such 

 purely mechanical mode of consideration ; we will therefore 

 merely repeat, that the simplicity of the physical principles of 

 explanation are better adapted to give a safe direction to our con- 

 jectures and further investigations, than if we were credulously to 

 trust to a transcendental mode of reasoning, without the aid of 

 earnest and profound reflection. 



In passing from these provisional remarks to the process of 



