56 THE BLOOD-GASES. 



Fernet, serum takes up slightly more than corresponds to the 

 pressure, and this is, perhaps, due to the trace of haemoglobin con- 

 tained in the plasma or the serum, and which is derived from the 

 solution of red corpuscles. 



(b.) Almost the total of the blood is chemically united, and, therefore, 

 not subject to the law of absorption. It is loosely united to the 

 haemoglobin of the red corpuscles, with which it forms oxylicemoglobin 

 (p. 29). 



The absorption of this quantity of O is completely independent of pressure; 

 hence, animals confined in a closed space until they are nearly asphyxiated, can 

 use up almost all the from the surrounding atmosphere. The fact of the union 

 being independent of pressure is proved by the following: The blood only gives 

 off copiously its chemically united O, when the atmospheric pressure is lowered 

 to 20 millimetres, Hg. (Worm Miiller) ; and, conversely, blood only takes up a 

 little more when the pressure is increased to 6 atmospheres (Bert). 



Physical Methods of obtaining from Blood. Notwithstanding 

 this chemical union between the Hb and 0, however, the total of the 

 blood can be expelled from its state of combination by those means 

 which set free absorbed gases (a.) by introducing blood into a torri- 

 cellian vacuum ; (b.) by boiling ; (c.) by the conduction of other gases 

 [H,N,CO or NO] through the blood, because the chemical union 

 of the oxyhsemoglobm is so loose that it is decomposed even by these 

 physical means. 



Chemical Reagents. Amongst chemical reagents the following re- 

 ducing substances ammonium sulphide, sulphuretted hydrogen, alkaline 

 solutions of sub-salts, iron filings, &c., rob blood of its (p. 30). 



With regard to the taking up of O, the total quantity of blood behaves 

 exactly like a solution of haemoglobin free from (Preyer.) The 

 amount of iron in the blood (0'55 in 1,000 parts) stands in direct 

 relation to the amount of Hb; this to the quantity of blood-corpuscles; 

 and this, in turn, to the specific gravity of the blood. The amount of 

 in the blood, therefore, is nearly proportional to the specific gravity 

 of the blood, and it is also in proportion to the amount of iron in the 

 blood. Picard affirms that 2*36 grammes of iron in the blood can 

 fix chemically 1 grrn. 0; while, according to Hoppe-Seyler, the pro- 

 portion is 1 atom iron to 2 atoms 0. 



When blood is kept long outside of the blood-vessels, the quantity of gradually 

 diminishes, and if it be kept for a length of time at a high temperature it may 

 disappear altogether. This depends upon decomposition occurring within the 

 blood. By this decomposition in the blood (cadaveric phenomenon), reducing 

 substances are formed which consume the 0. All kinds of blood, however, do not 

 act with equal energy in consuming 0, e.gr., venous blood from active muscles acts 

 most energetically, while that from the hepatic vein has very little effect. C0 2 

 appears in the blood in place of the O, and the colour darkens. The amount of 

 COa produced is sometimes greater than that of the consumed. 



