142 THE BLOOD. 



measured amount of carbonic oxide (mixed with oxygen) ; then drew 

 off a measured quantity of blood, and determined the amount of carbonic 

 oxide this contained ; the amount in the whole of the blood in the body 

 would be in the same proportion, and the quantity of blood could thus 

 be calculated. The result arrived at by these two methods is that the 

 blood is equal to one-eleventh to one-fourteenth of the body weight 

 (about 5 1 kilos, in a man of 70 kilos.). 



Colour : laking of blood. The colour of the blood varies in different 

 parts of the vascular system. The differences are dependent upon the 

 amount of oxygen in combination with the haemoglobin. The colour 

 also becomes altered by any reagent or circumstance which tends to 

 cause the haemoglobin to pass out fr^m the corpuscles into the circum- 

 jacent fluid. When this is brought about, the blood loses its opaque 

 appearance and becomes transparent and of a laky tint. Such " laky " 

 blood is readily produced by the addition of distilled water, and also by 

 water holding neutral salts in solution up to a certain percentage ; which 

 percentage varies for different salts, and also, with the same salts, for the 

 blood of different animals. A solution containing just such a percentage 

 of salt as suffices to keep the corpuscles unaltered in form, and without 

 removal of any of their haemoglobin, is " isotonic " ; l solutions below and 

 above such strength are respectively " hypisotonic " and " hyperisotonic." 2 

 For human blood, a solution of common salt is isotonic with a percentage of 

 0'9 ; for defibrinated ox blood, with 0'6, and about the same for frog's blood. 

 Very slight differences of external condition will tend to alter the per- 

 meability of the blood corpuscles both for haemoglobin and for other 

 substances. A minute diminution in the alkalinity, such as is produced 

 by the addition of 0'003 per cent. HC1, so alters the permeability as to 

 cause proteid to pass from the corpuscles into the serum, and chlorides or 

 phosphates to pass into the corpuscles from the serum ; a minute increase 

 of alkalinity has the opposite effect. The passing of oxygen and carbonic 

 acid respectively through blood produces like physical changes, and it has 

 been suggested that these changes may come into operation in connection 

 with the metabolic exchanges in the capillaries. 3 These osmotic effects 

 alter the total volume of the corpuscles as compared with the plasma ; 

 the proportional alterations are determined by centrifugalising blood, 

 and then measuring the respective amounts of subsided corpuscles and 

 superjacent plasma. 4 Laky blood is produced not only by water and 

 dilute solutions of neutral salts, but also by many other reagents or con- 

 ditions, such as crushing of the corpuscles, freezing and thawing the 

 blood, and also by the action of acids, of alkalies, of bile salts, of ether and 

 chloroform, of heat and electricity. 5 In all cases the permeability of 

 the envelope of the red corpuscle (see p. 154) becomes altered either by 

 mechanical means or by the solution of one or more of its constituents, 



1 Having the same osmotic pressure (de Yries, Ztschr. f. physikal. Chem., Leipzig, 1888, 

 Bd. ii. S. 415). 



2 Hamburger, Arch. f. PhysioL, Leipzig, 1886, S. 476 ; Ztschr. f. Biol., Miinclien, 1890, 

 Bd. xxvi. S. 414. 



3 Hamburger, Ztschr. f. Biol., Mitnchen, 1892, Bd. xxviii. S. 405; Arch. /. PhysioL, 

 Leipzig, 1892, S. 513 ; 1893, Suppl. Heft, S. 153 ; and Verhandel. d. k. AJcad. v. Wetensh. 

 te Amsterdam, 1897, S. 368. 



4 Koeppe, Arch.f. PhysioL, Leipzig, 1895, S. 154 ; Hedin, Skandin. Arch.f. PhysioL, 

 Leipzig, 1895, Bd. v. S. 207 and 238. 



For literature of this, see Rollett in Hermann's "Handbuch der Physiologic," Bd. iv. 

 S. 14. 



