262 DIGESTION. 



tolerably closely with the equivalents of diffusion. The definite 

 attraction towards water, which we see so variously expressed in 

 the above cases by solid soluble substances, and the attraction 

 shown in the last-named case of solid insoluble bodies to water, 

 equally lead us into a domain of inquiry, in which we receive no 

 aid whatever from empirical bases ; although the long-known, as 

 well as the more recent investigations regarding hygroscopicity by 

 Bliicher,* by Schwede,t and by Buchheim,J and the provisional 

 results obtained by Briicke, Liebig, and Ludw T ig, agree in showing 

 that even in this relation between the three important bodies 

 already referred to, the most essential differences are observable in 

 respect to the attraction towards water. No physiologist can 

 doubt that all the relations of solid bodies to water must be involved 

 in the explanation of the phenomena of absorption and of the 

 mechanical and chemical metamorphosis of matter ; but even if 

 we admit that absorption is nothing more than a function of these 

 various relations, we are not thereby enabled to explain the process 

 of absorption, for we have not yet succeeded in expressing by a 

 mathematically demonstrable formula any of the different kinds of 

 attraction between water and solid bodies, or of establishing the 

 relations which exist amongst them. For how is any explanation 

 practicable, or, in other words, how can we refer phenomena to 

 laws, when we are ignorant of the laws themselves ? We may, 

 however, conclude from the scanty facts before us, that the move- 

 ments of soluble matters within the living organism, and more 

 especially the phenomena of absorption, must be supposed to 

 depend upon certain physical laws. Thus tremble and fall the last 

 feeble supports of the old and naive belief in an instinct, or a cer- 

 tain spiritual capacity of the absorbing organs. The time may, 

 however, come, and perhaps is not very remote, when we may 

 include amongst " comprehensible ideas 5 ' the properties of every 

 substance whose relation to the animal body may be brought 

 into question ; when the zoological department of physiological 

 chemistry will no longer be limited to the enumeration of a few 

 qualities of bodies, either arbitrarily or accidentally selected, but 

 will indicate all without exception the coefficients of condensation 

 of their solutions as well as their absolute solubility, their diffusi- 

 bility as well as their volatility, their endosmotic as well as their 

 chemical equivalent, their hygroscopicity as well as their fusibility, 



* Pogg. Ann. Bd. 50, 8. 541-562. 



f 1 De Hygroscopicitate, diss. inaug. Dorp. Livon. 1851. 



t Arch. f. physiol. Heilk. Bd. 12, S. 217-243. 



