294 PHYSIOLOGICAL PHYSICS. [chap. xxui. 



the differences of pressure during both acts being so 

 considerable. A transference of carbonic acid gas 

 from the blood into the air cells would also be ac- 

 complished specially during inspiration, since during 

 expiration the pressures approach one another. 

 The problem, however, is not the simple one thus 

 represented, for between the blood and the air is 

 the organic septum, moistened on one side by the 

 blood, and on the side of the air also moist, like 

 the rest of the mucous lining of the lungs. The mem- 

 brane, therefore, separates two solutions containing 

 different quantities of the same gases, and the process 

 of osmosis, already discussed in chap, xxii., enters as 

 an agent in the transference. A second and more im- 

 portant modifying agent, however, must also be 

 considered. Blood, deprived of its red blood-cor- 

 puscles, is found to absorb about the same quantity of 

 oxygen as water, and in accordance with the law of 

 pressures, but a much less quantity than the usual 

 oxygen of the blood. Further, blood not deprived of 

 its corpuscles is found not to absorb oxygen in ac- 

 cordance with Dalton's law of pressures. If placed in 

 a receiver, which is gradually exhausted, the blood does 

 not yield up its gases in proportion as the rarefaction 

 proceeds, but when a certain degree of exhaustion has 

 been reached a large quantity rapidly comes off. The 

 haemoglobin of the red blood-corpuscles explains these 

 variations from the physical law. It is found to have 

 a strong affinity for oxygen. If, itself free of 

 oxygen, except what forms part of its chemical consti- 

 tution, it be exposed to an atmosphere of oxygen, it 

 at first rapidly absorbs a considerable quantity, and 

 afterwards does not absorb amounts increasing with 

 increasing pressures according to Dalton's law. What 

 it does absorb can be dissociated from it by exposing 

 it to a sufficiently low pressure. Oxygen seems thus 

 to form a loose chemical combination with the hsemo- 



