THE RESPIRATORY SYSTEM, 385 
absorb under pressure, it is found that the amount taken up 
depends on the quantity of the particular gas present independ- 
ent of the presence or quantity of the others; thus, if water 
be exposed to a mixture of oxygen and nitrogen, the quantity 
of oxygen absorbed will be the same as if no nitrogen were 
present—i.e., the absorption of a gas varies with the partial 
pressure of that gas in the atmosphere to which it is exposed. 
But whether blood, deprived of its gases, be thus exposed to 
oxygen under pressure, or whether the attempt be made to 
remove this gas from arterial blood, it is found that the above- 
stated law does not apply. 
When blood is placed under the exhaustion-pump, at first 
very little oxygen is given off; then, when the pressure is con- 
siderably reduced, the gas is suddenly liberated in large quan- 
tity,and after this comparatively little. A precisely analogous 
course of events takes place when blood deprived of its oxygen 
is submitted to this gas under pressure. On the other hand, 
if these experiments be made with serwm, absorption follows 
according to the law of pressures. Evidently, then, if the oxy- 
gen is merely dissolved in the blood, such solution is peculiar, 
and we shall presently see that this supposition is neither neces- 
sary nor reasonable. 
H2MOGLOBIN AND ITS DERIVATIVES. 
Heemoglobin constitutes about # of the corpuscles, and, 
.though amorphous in the living blood-cells, may be obtained 
in crystals, the form of which varies with the animal; in- 
deed, in many animals this substance crystallizes spontane- 
ously on the death of the red cells. It is unique among albu- 
minous compounds in being the only one found in the animal 
body that is susceptible of crystallization. Its estimated com- 
position is: 
Carboricicas seni ines eee ewes 53°85 
Hydrogen susasssvesksnw tive ey adew cusps 7°32 
Nitrogen sss wend vade ies Mewes Siew 16°17 
OXY LON ee ee itidel seek cee Kee sets 21°84 
TrOnng sc ceaacy dew oe nase ee w Laie ee 43 
Sulphur sass aussi weteaeumawa ww sea "39 
together with 3 to 4 per cent of water of crystallization. 
The formula assigned is: CswHsoOnNinFeSs. The molecular 
constitution is not known, and the above formula is merely an 
approximation, which will, however, serve to convey an idea 
25 
