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 oh 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 from 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 
- 9 ; for defibrinated ox blood, with - 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 Gon- 
dii inns, 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 (deVries, Ztschr. f. physikal. Chcm., Leipzig, 1888, 
Bd. ii. S. 115). 
2 Hamburger, Arch. f. Physiol., Leipzig, 1886, S. 476 ; Ztschr. f. Biol., Munchen, 1890, 
Bd. xxvi. S. 414. 
3 Hamburger, Ztschr. f. Biol., Munchen, 1892, Bd. xxviii. S. 405; Arch. f. Physiol., 
Leipzig, 1892, S. 513 ; 1893, Suppl. Heft, S. 153 ; and Verhandel. d. k. Akad. v. Wetensh. 
te Amsterdam, 1S97, S. 368. 
4 Koeppe, Arch. f. Physiol., Leipzig, 1895, S. 154 ; Hedin, Skamdin. Arch./. Physiol., 
Leipzig, 1895, Bd. v. S. 207 and 238. 
5 For literature of this, see Rollett in Hermann's "Handbuch der Physiol ogie," Bd. iv. 
S. 14. 
