i 44 THE BLOOD. 
The methods which have been used for determining the specific gravity of 
the blood are— (1) that of directly weighing a sample (pycnometer), and (2) 
Roy's method. The latter is by far the readiest, and, for small quantities of 
blood, the more accurate. It consists in transferring minute drops of blood to 
glycerine and water, mixed in varying proportions, and forming a graduated 
series of liquids of different and known specific gravities, and in observing in 
which mixture the drop tends neither to rise nor to fall. The method has been 
modified by the use of benzene and chloroform mixtures instead of glycerine and 
water, and also by placing the drop of blood in such a mixture, and adding benzene 
. >r chloroform, as the case may be, until the drop remains exactly suspended, 
tending neither to rise nor fall ; the specific gravity of the mixture is then 
taken (Hammerschlag). It may lie doubted, however, whether these modifica- 
tions are more readily applied, or more accurate than Roy's method. 
Reaction. — The alkaline reaction of the blood is easily recognised, in 
spite of its red colour, byapplyinga drop of blood to tin- surface of a piece 
of glazed litmus paper, and after half a minute wiping away the blood 
with a piece of clean linen, wotted with distilled water or with neutral 
salt solution. The part of the paper which was covered by the blood 
will show a blue patch. 1 A comparison may be made between different 
samples of blood, by using a series of litmus papers which have been 
reddened by Btandard acid of different strengths. 2 For estimating the 
amount of its alkalinity the blood is mLxed in small measured quantity 
with a solution of sulphate of soda, containing a definite amount of 
tartaric acid, 3 titrated against sodium hydroxide, and the mixture found 
which is exactly neutral to glazed litmus paper. Tested by this method, 4 
the alkalinity "of human blood is found to be equal to about 0-200 
grms. of -odium hydroxide per 100 c.c. blood. 5 There appears to be 
a diurnal variation, the alkalinity being lowest in the morning, and 
gradually rising in the afternoon, becoming less again in the evening. It 
rises during digestion. 6 It is dimirrished by muscular work, especially 
with a diet containing little or no proteid. 7 On the other hand, with a 
diet rich in proteids, it undergoes very little alteration. In accordance 
with this, it is found that carnivora resist an artificial diminution of the 
normal blood alkalinity (such as would be caused by giving dilute mineral 
1 Schafer, Journ. Physiol., Cambridge and London, 1881, vol. iii. i>. 292. 
3 Haycraft and Williamson, !'>■■„-. Roy. Soc. Edin., 1888, vol. xv. p. 396. For fallacies 
in the clinical application of this method, see Hutchison, Lancet, Loudon, 1896, vol. i. 
P- 616 - ™ • .. • 
;; Lassar, Arch. /. J. ges. Physiol., Bonn, 1S74, Bd. ix. S. 44 ; Droum (These, Pans, 
1892) used oxalic acid. 
4 The principle of the method is due to Zuntz, who, however, used phosphoric acid 
(Centralbl. f. 0. med. Wissensch., Berlin, 1867, S. SOI); but the details were greatly 
improved by Lamlois ("Real-Eucyklopadie," Aufl. 2, Bd. iii., article "Bint"). For other 
methods of estimating the alkalinity, see v. Limbeck. Wien. med. BL, 1895, S. 295 ; and 
Schntz-Schultzerstein, Centralbl. f. d. med. Wissensch., Berlin, 1894, Bd. xxxii. S. 801. 
According to Mayer (A rch.f. exper. Path. u. Pharmakol., Leipzig, 1883, Bd. xvii. S. 304), 
all titration methods are unreliable with blood, but his conclusions have not been accepted 
by most physiologists. 
5 Freudberg, Virchows Archiv, 1891, Bd. exxv. S. 566, gives an average alkalinity in 
health of - 200 to # 240 gnn. XaHO per cent. Jeffries (Boston Med. and S. Journ., 1889) 
obtained about 0*200 as the average, and Drouin about 0'206. v. Jaksch. (Ztschr.f. hi 'in. 
Med., Berlin. 1SSS. Bd. xiii. S. 353) found the alkalinity of normal human blood as high 
as 0-200 to 0-300.; Loewy (Arch. f. d. ges. Physiol., Bonn, 1894, Bd. lviiii. S. 498), working 
with "laked" blood, found its alkalinity =0 "449 grms. XaHO ; and Berend (Ztschr.f. 
Htilk., Berlin, 1896, S. 351) obtained an alkalinity from "laked" blood of 0'450 to 0*500. 
6 Peiper, Virchow'sA 1 - s 9, Bd. cxvi. S. 337. 
7 Cohnstein, Virchow's Archiv, 1892, Bd. exxx. S. 332. See also Geppert u. Zuntz, 
Arch.f. d. ges. Physiol., Bonn, 1888, Bd. xlii. S. 233, and Peiper, loc. cit. 
