THE ACTION OF DIURETICS. 
349 
Why do the alkaline salts purge in large doses, and produce 
diuresis in fractional doses 1 We subjoin the explanation given 
by Justus Liebeg. 
This celebrated chemist lays it down as a principle, that the 
animal membranes no longer absorb saline solutions when they 
themselves are more rich in saline principles than the blood which 
circulates through their vessels. Those which are highly concentrated, 
such as saline purgative drinks for example, give rise, even within 
the intestine, to an action of exosmose, by which the serum of the 
blood is drawn out of its vessels by the saline solution, which is 
highly attractive of water. From this effect results an abundant 
serous exhalation, and, as a consequence, purgation. Saline solu- 
tions, on the contrary, which are less charged with salts than the 
serum of the blood, are attracted by this latter ( endosmme ) through 
the intestinal mucous membrane, whence it passes into the blood, 
and quits through the urinary passages*. 
M. Poiscuille, in studying the endosmose of the serum of the 
blood and saline solutions more or less concentrated, has succeeded 
in experimentally demonstrating the exactitude of the theory of 
Liebeg. He has proved that endosmose always takes place from 
serum to saline solution as often as the latter was sufficiently con- 
centrated. Thus the neutral tartrate of potass, the sulphate of soda, 
the sulphate, nitrate, and phosphate of potass, marine salt, ioduret 
of potassium, alum, ever attract the current of serum to them, and 
the more powerfully as the saline solution is more concentrated ; 
on the contrary, reducing the salts down to very weak proportions, 
as, for example, one part of phosphate of soda to one hundred 
parts of water, the current becomes turned from the salt to the 
serum. 
This physiologist compares the effects produced in endosmose 
to what is passing upon the surface of the intestinal tube under 
the influence of divers medicamentary principles. Does anybody 
administer an alkaline salt in concentrated solution 1 — the serum of 
the blood escapes through its capillary vessels and bedews the in- 
testinal villosities; then is endosmose of the serous parts of the 
blood in the interior of the intestine an afflux of fluids, and, in con- 
sequence, follows purgation. On the contrary, if the solution is 
diluted, there is endosmose the other way : the salt penetrates 
through into the circulation, and escapes through the kidneys by 
producing diuresis.! 
So that it is satisfactorily demonstrated that the alkaline salts 
may prove purgative or diuretic, indifferently, according to the 
doses in which they are given. From this fact results an im- 
portant precept in pharmacology, which is, that we lose more than 
* Liebig: Chemistry applied to Vegetable Physiology and Agriculture. 
t Compte-Rendu de l’Academie des Sciences, vol. xix, p. 994. 
VOL. XXIII. 3 A 
