CONDITION OF THE GASES IN THE BLOOD. 467 



tion. The proportion which they are capable of containing 

 is to a certain degree absolute, and not dependent upon phys- 

 ical conditions, such as pressure, which invariably have an 

 influence on the proportion of gas merely held in solution by 

 liquids. The proportion of oxygen in the blood cannot be 

 increased by pressure, nor is it diminished by reduction 

 of the pressure, until it approaches a vacuum. 1 The fact 

 that the blood-corpuscles are capable of consuming oxygen 

 and giving off carbonic acid is an additional argument in 

 favor of the union of these anatomical elements with the 

 gas, though this union is very feeble and easily disturbed. 

 The plasma will absorb a certain quantity of oxygen, and its 

 action in respiration seems to be intermediate ; it first takes 

 oxygen from the air and then gives it up to the corpuscles. 



Carbonic acid is more easily exhaled from the blood than 

 oxygen. It was this principle which was obtained by those 

 who first succeeded in extracting gas from the blood. While 

 there is every reason to suppose that oxygen is in combina- 

 tion with the blood-corpuscles, carbonic acid seems to be in a 

 condition of simple solution, and is contained more especially 

 in the plasma. What may be considered as the free carbonic 

 acid of the blood behaves in all regards like a gas simply held 

 in solution. The view that it is held in solution chiefly in the 

 plasma is sustained by the fact that serum will absorb more 

 carbonic acid than an equal volume of defibrinated blood. 2 



Liebig has shown that the phosphate of soda, one of the 

 constituents of the blood, influences to a remarkable degree 

 the quantity of carbonic acid which can be held in solution 

 by any liquid. One hundredth of a part of this salt in pure 

 water will double its capacity for dissolving carbonic acid. 3 



1 The fact that oxygen is exhaled from the blood in vacua is not an argument 

 against the view that it enters into feeble combination with the blood-corpuscles ; 

 for it is well known that many distinctly recognized chemical combinations are 

 disturbed by the same means. For example, a vacuum is capable of disengaging 

 from some of the bicarbonates one equivalent of carbonic acid. 



2 LONGET, Traite de Physiologic, Paris, 1861, tome i., p. 494. 



3 MILNE-EDWARDS, Physiologic, tome i., p. 471. 



