The first, according to Bergmann, has a density of 1.006. It contains in each pint 192.8 grains of solid matter. Out of this, 180 grains consist of Sulphate of Magnesia.
Sea-water has a specific gravity of 1.026, and its solid contents are about 3.5 per cent. But Dr. G. Bird says that less than five per cent. of saline matter constitutes a liquid diuretic.
These, then, are strong reasons against this idea considered merely as a theory. But it can readily be put to the proof. With this purpose I have made the following experiments. As far as they are concerned, they seem to show that salines are in all cases absorbed, and that whether they are subsequently excreted through the kidneys or by the bowels depends more on the quantity administered than on the degree of dilution of the dose.
EXP. 1.--A sufficient quantity of white sugar was dissolved in four ounces of water to raise its specific gravity to 1.028, that of the serum of the blood. Two drachms of sulphate of magnesia were dissolved in another ounce of water, so that the solution measured nine fluid drachms, and had a density of 1.060. This heavier solution was introduced into an open wide tube, closed completely below by a clean piece of bladder. It was introduced into a small vessel containing the solution of sugar, and arranged so that the height of the two liquids should correspond. After three days, the inner solution measured two drachms more, and the specific gravity had sunk to 1.050. The outer solution, after making up exactly the loss by evaporation, was found to have risen in density to 1.040. On adding a small quantity each of the solutions of phosphate of soda and carbonate of ammonia, a copious precipitate took place, indicating the presence of magnesia. Thus it appeared that the fluids passed both ways, some of the heavy solution of magnesia finding its way through to the lighter solution of sugar. The tendency of this process was evidently to an equalization of their densities, both by endosmose one way and by exosmose the other. Thus, apparently, would it be with a saline purgative, and with the serum of the blood.
EXP. 2.--Three drachms of Sulphate of Magnesia (a very mild purgative dose) were dissolved in ten ounces of water, and thus administered to a healthy young man. It produced, after some time, slight purging, and some diuresis. The urine, when tested, contained only a very little more than the usual quantity of magnesia. The quantity in the dose was less than five per cent. of the solution, and thus, according to the endosmotic theory, should have produced no purging.