132 RESPIRATION 



firmed these observations by experiments on the human subject. Not- 

 withstanding the conflicting testimony of physiologists, there can be little 

 doubt that under ordinary physiological conditions there is an exhalation 

 of a small quantity of nitrogen by the lungs. 



CHANGES OF THE BLOOD IN RESPIRATION (HEMATOSIS) 



There is a marked difference in color, composition and properties, 

 between the blood in the arteries and in the veins, the change from 

 venous to arterial blood being effected almost instantaneously in its 

 passage through the lungs. The blood which goes to the lungs is col- 

 lected from all parts of the body and presents great differences in its 

 composition in different veins. In some veins it is almost black, and in 

 some it is nearly as red as in the arteries. In the hepatic vein it con- 

 tains sugar, and its nitrogenous constituents and the corpuscles are 

 diminished ; in the portal vein, during digestion, it contains matters 

 absorbed from the alimentary canal ; and finally, there is every reason 

 to suppose that parts which require different substances for their nutri- 

 tion and produce different excrementitious matters exert different 

 influences on the constitution of the blood which passes through them. 

 After this mixture of different kinds of blood has been collected in the 

 right side of the heart and passed through the lungs, it is returned to 

 the left side and sent to the system, and as arterial blood, it has a nearly 

 uniform composition. The change, therefore, which the blood under- 

 goes in its passage through the lungs, is the transformation of the mixture 

 of venous blood from all parts of the organism into a liquid of uniform 

 character, which is capable of nourishing every tissue and organ of the 

 body. 



The capital phenomena of respiration, as regards the air in the lungs, 

 are loss of oxygen and gain of carbon dioxide, the other phenomena 

 being comparatively unimportant. As the blood is capable of absorb- 

 ing gases, the essential changes which it undergoes in respiration are to 

 be looked for in connection with the proportions of oxygen and carbon 

 dioxide before and after it has passed through the lungs. 



The elements of the blood which absorb the greatest part of the 

 oxygen are the red corpuscles. While the plasma will absorb, perhaps, 

 twice as much gas as pure water, it has been shown that the volume of 

 oxygen fixed by the corpuscles is about twenty-five times that which is 

 dissolved in the plasma (Fernet, Lothar Meyer). 



Analysis of the Blood for Gases. In disengaging and estimating the 

 gases of the blood, it is necessary to complete the analysis as soon as 

 possible after the blood has been drawn, for the reason that delay in- 



