EDITORIAL OBSERVATIONS. 413 
logical phenomena which have hitherto been involved in much ob¬ 
scurity. 
“ The stomach of an animal is a dialysing’ apparatus, iu which the 
soluble food is dialysed, and the insoluble food digested under the 
influence of crystalloids, supplied through the coats of the stomach by 
diffusion. 
“The abundant flow of free hydrochloric acid into the stomach, 
which occurs during the process of digestion, may be accounted for by 
referring to the analogous action in tiie dialysis of the basic chlorides 
of colloidal substances, such as oxide of iron, alumina, &c. In such 
cases the acid leaves the colloid and passes in the free state through 
the septum, and by a similar action hydrochloric acid is probably sup¬ 
plied to the stomach. 
“The nutritive constituents of food belong to the class of colloids, 
which are retained in the stomach while the act of digestion proceeds 
under the influence of crystalloids that are dialysed into that organ, 
and then pass on to undergo new changes connected with absorption, 
assimilation, and excretion. 
“The action of medicines must be considerably influenced by the 
state in which they exist as colloids or as crystalloids. Thus, iron in 
the state of chloride, sulphate, or other crystalloidal salt, would be 
diffused through the coats of the stomach, but not so if in the state of 
a colloid, such as basic chloride, or basic nitrate, in which state it 
.would pass into the intestines, exerting its action probably throughout 
the entire length of the alimentary canal. Is it not from this difference 
in their action that some preparations of iron colour the excrements, 
while others do not? 
“ It will be important to determine the diffusive power of many pre¬ 
parations used in medicine, as a guide to the physician, and it may be 
found desirable to devise new preparations, where such are deficient, 
to represent certain medicinal agents in the colloidal as well as the 
crystalloidal state. 
“ Not only the physiologist, but also the geologist, derives important 
aid from the study of liquid diffusion in the explanation of phenomena 
occurring in his department of science. The question is often asked, 
what is the origin of flint and other forms of silica, of oxide of iron, 
of alumina, and other substances, which, although usually accounted 
insoluble, are found in nature under circumstances clearly indicating 
that they have been deposited from solution. This question may be 
answered by referring to the solutions of all these substances which are 
obtained by dialysis.’’ 
The importance of this mode of analysis cau scarcely be 
questioned; and already, in the hands of men of science, it 
is developing some important facts, and bids fair to be the 
means of obtaining a new class of pharmaceutical pre¬ 
parations, occupying an intermediate place between in¬ 
fusions, decoctions, and extracts, and the more pure and 
certain, but costly active principles of vegetables; nor need 
it be confined to these. 
