1890-91.] Dr Haycraft on Specific Gravity of the Blood. 251 
A New Method for the Estimating the Specific Gravity of 
the Blood. By John Berry Haycraft, M.D., D.Sc. 
(. Physiological Laboratory , University of Edinburgh.) 
(Read January 19, 1891.) 
The method of Boy for determining the specific gravity of the 
blood is a very excellent one, and is capable of yielding sufficiently 
accurate results. Over thirty bottles containing mixtures of 
glycerine and water of different specific gravity, ranging from 
1*030 to 1*070, are used for the estimation, and a drop of blood to 
be tested is placed in a sample of one of these fluids. If the drop 
sinks it is heavier, if it floats it has a lower specific gravity, and 
then another drop of the same blood is tested until by a few experi- 
ments the exact specific gravity is determined. 
It might be imagined that this method is more difficult to carry 
out than it really is, and that it requires many attempts on the 
part of the experimenter, and the loss of much blood, before the 
specific gravity is finally settled. This is no doubt true in the case 
of a patient examined for the first time, but afterwards, knowing 
beforehand what the specific gravity is likely to be, it is easy, with 
one or two trials, to find out if any change in the specific gravity 
has occurred. 
The chief objection to the method is, however, the cumbrous 
nature of the apparatus required, which would render it useless for 
the requirements of private practice, although undoubtedly of much 
value in the Hospital and Laboratory. > 
The method I venture to introduce has this advantage that the 
apparatus used is quite portable, requiring no more room than the 
space occupied by a small pocket case. The method is accurate, 
requires only a single drop of blood, and, moreover, it is perhaps 
more quickly done than that of Boy. 
Two mixtures of benzyl chloride (sp. gr. 1*100) and toluol 
(sp. gr. 0*8706) are made, one (A) having a specific gravity of 1*070, 
and the other (B) having a specific gravity of 1*020. With a cubic 
centimetre pipette graduated to yj^th c.cm., one c.cm. of (A) is 
