SPECIFIC GRAVITY. 143 



and the haemoglobin is thereby permitted to diffuse into the circumjacent 

 fluid. 



Specific gravity. The specific gravity of the blood varies in health 

 within small limits, namely, for men, 1057 to 1066 ; for women, 1054 to 

 106 1. 1 According to Lloyd Jones, 2 it is lower than this in women, averaging 

 1051*5 between the ages of 35 and 45, whereas in men of the same age it 

 averages 1058*5. It falls a little when much fluid is injected, and is raised 

 a little by profuse perspiration, but the changes thus produced are very 

 small. 3 It is slightly less in children than in adults, but it is higher in 

 the foetus than in the mother ; and it is highest in the child at term, in 

 which it is 1066, the specific gravity of the maternal blood being then 

 only about 1050. 4 The diurnal variations are normally so small as to be 

 almost negligeable. Passive congestion of the part from which the speci- 

 men examined is taken increases the specific gravity, whereas active con- 

 gestion lowers it. It varies also according to the part, of the body from 

 which it is taken, such variation being probably due to accidental admix- 

 ture with lymph. Thus Lloyd Jones found a difference of as much as 

 three or four per 1000 between blood from the finger (lower) and blood 

 from the skin over the shin (higher). Of the animals examined, it has 

 been found higher in birds than mammals, and to vary somewhat in these 

 animals in different species. The variations in age and sex are closely 

 related to variations in the amount of haemoglobin. Saline solution 

 (NaCl, 075 per cent.) injected in quantity into the blood only depresses 

 the specific gravity for a short time. The specific gravity of blood from 

 a vein is practically the same as that from the corresponding artery, if 

 care be taken to avoid venous congestion. 5 



The specific gravity of the blood falls after the removal of blood, 

 doubtless from absorption of the specifically lighter lymph from the 

 tissues. It subsequently (in about six hours) not only returns to 

 normal, but even rises above normal ; after about twelve hours it has 

 permanently recovered its normal specific gravity. 6 



Almost any operation performed upon an animal, especially one 

 involving exposure or irritation of a serous membrane, will produce an 

 increased percentage of corpuscles (polycythaemia), or a corresponding 

 diminution of plasma. This is due, not to increased formation of cor- 

 puscles, but to exudation of plasma in the inflamed or irritated part. 7 



1 Haramersclilag, Ztschr. f. Uin. Med., Berlin, 1892, Bd. xx. S. 444. The results of 

 other workers will be found in this paper. For the older literature, see Kollett, op. cit., S. 

 134. The numbers given by Peiper (CentralU. f. Uin. Med., Bonn, 1891, Bd. xii. S. 217) 

 are 1*055 as the average for men, and 1 '053 for women. 



2 Journ. Physiol., Cambridge and London, 1888, vol. viii. p. 1. 



3 Schmaltz, Arch. f. Uin. Med., Berlin, 1891, Bd. xlvii. S. 145; Grawitz, Ztschr. f. 

 Uin. Med., Berlin, Bd. xxi. S. 459, and Bd. xxii. S. 411. 



4 Lloyd Jones, op. cit. 



5 Cohnheim and Zuntz, Arch. f. d. ges. Physiol., Bonn, 1888, Bd. xlii. S. 303. 

 For the effects of varying conditions of health and disease upon the specific gravity 

 of the blood consult Lloyd Jones, Journ. Physiol., Cambridge and London, 1891, vol. xii. 

 p. 299, where a large number of observations are accumulated. Lloyd Jones worked by 

 Roy's method, Scholkoff (Diss., Bern, 1892), working by a different method (pycnometer), 

 has obtained very similar results. Both observers agree in the important fact that the 

 specific gravity varies as a rule pari passu with the richness in haemoglobin. For the 

 specific gravity in different animals, and for variations experimentally induced, see Sher- 

 rington and Copeman, Journ. Physiol., Cambridge and London, 1893, vol. xiv. p. 52. 



6 Ziegelroth, Virchows Archiv, 1895, Bd. clxi. S. 395. 



7 See on this subject, Lowit, "Studien z. Phys. u. Path. d. Blutes," Jena, 1892; W. 

 Hunter, Journ. Physiol., Cambridge and London, 1890, vol. xi. S. 115; Sherrington and 

 Copeman, Joe. cit. ; Sherrington, Proc. Roy. Soc. London, 1893, vol. Iv. p. 161. 



