On the Variations in the Specific Gravity of the Blood in Health

THE present paper aims at giving an account of a number of observations which I have recently made by a method identical in principle with that suggested by Prof. Roy' for studying the variations in the specific gravity of the blood. The original method employed by Prof. Roy consisted in introducino a drop of the blood to be examined into a mixture of glycerine and water of known specific gravity, observing whether the blood tended to rise or sink in the solution. If the blood tended to rise, it was assumed that it was of lower specific gravity than the fluid in which it was placed; if the blood sank it was regarded as heavier than the solution. In the formier case another drop of the blood was placed in a mixture of glycerine and water of lower specific gravity than the one first employed, it being again observed whether the blood rose or sank. By having ready to hand a considerable number of such solutions of glycerine in water of different specific gravities, it was not difficult to find one in which the blood which was being examined neither rose nor sank, and as its specific gravity was known the specific gravity of the blood examined was thus found. The degree of accuracy of such a method as this will depend partly on the number of standard solutions employed. For many observations sufficient accuracy in this particular is arrived at by having at hand a separate solution for each degree of the ordinary specific gravity scalewithin those limits within which the specific gravity of the blood varies in different individuals at different timnes. These limits were found to