144 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 

 or 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 be 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, by applying a drop of blood to the surface of a piece 

 of glazed litmus paper, and after half a minute wiping away the blood 

 with a piece of clean linen, wetted 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 standard acid of different strengths. 2 For estimating the 

 amount of its alkalinity the blood is mixed 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 O200 

 grms. of sodium 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 diminished 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. p. 292. 



2 Haycraft and Williamson, Proc. Roy. Soc. Edin., 1888, vol. xv. p. 396. For fallacies 

 in the clinical application of this method, see Hutchison, Lancet, London, 1896, vol. i. 

 p. 616. 



3 Lassar, Arch. f. d. ges. PhysioL, Bonn, 1874, Bd. ix. S. 44; Drouin (These, Paris, 

 1892) used oxalic acid. 



4 The principle of the method is due to Zuntz, who, however, used phosphoric acid 

 (CentralbL f. d. med. Wissensch., Berlin, 1867, S. 801) ; but the details were greatly 

 improved by Landois ("Real-Encyklopadie," Aufl. 2, Bd. iii., article "Blut"). For other 

 methods of estimating the alkalinity, see v. Limbeck, Wi&n. med. BL, 1895, S. 295 ; and 

 Schutz-Sehultzerstein, CentralbL f. d. med. Wissensch., Berlin, 1894, Bd. xxxii. S. 801. 

 According to Mayer (Arch.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 Freudb'erg, Virchow's Archiv, 1891, Bd. cxxv. S. 566, gives an average alkalinity in 

 health of '200 to 0'240 gmi. NaHO 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. Jclin. 

 Med., Berlin, 1888, Bd. xiii. S. 353) found the alkalinity of normal human blood as high 

 as 0'260 to 0'300.; Loewy (Arch. f. d. ges. PhysioL, Bonn, 1894, Bd. Iviiii. S. 498), working 

 with "laked" blood, found its alkalinity =0 '449 grms. NaHO ; and Berend (Ztschr.f. 

 Heilk., Berlin, 1896, S. 351) obtained an alkalinity from "laked" blood of 0'450 to 0'500. 



6 Peiper, Virchow's Archiv, 1889, Bd. cxvi. S. 337. 



7 Cohnstein, Virchow's Archiv, 1892, Bd. cxxx. S. 332. See also Geppert u. Zuntz, 

 Arch.f. d. ges. PhysioL, Bonn, 1888, Bd. xlii. S. 233, and Peiper, loc. cit. 



