ANALYSIS OF THE BLOOD FOR GASES 133 



volves a disappearance of a considerable quantity of oxygen, which is 

 replaced by carbon dioxide. This accounts for the indefinite results ob- 

 tained by the earlier observers. Modern experimenters make use of the 

 mercurial gas-pumps, either of Ludwig or of Pfliiger, in which all the 

 gases of the blood are disengaged by removing atmospheric pressure. 

 By means of a " froth-chamber," the gases can be collected and analyzed 

 with but little loss of time ; but it is probable that there is always a slight 

 error in estimates, made in this way, of the relative proportions of oxygen 

 and carbon dioxide, the proportion of oxygen being too small, and of 

 carbon dioxide, too large. Nevertheless, the results obtained by this 

 method correspond pretty closely with what is known of the nature of 

 the respiratory process; and analyses of the blood taken at different 

 times show variations in the quantities of oxygen in the arterial blood 

 and of carbon dioxide in the venous blood, corresponding with some of 

 the variations that have been noted in the loss of oxygen and gain of 

 carbon dioxide in the air in respiration. Nearly all the gases contained 

 in the blood may be disengaged by means of the gas-pump, but accord- 

 ing to most observers, a small quantity of carbon dioxide remains in the 

 blood in combination. This may be removed by the introduction into 

 the apparatus of a small quantity of tartaric acid. It was justly remarked 

 by Bert, that as the apparatus for the exhaustion of air has been made 

 more and more nearly perfect, the quantity of carbon dioxide in combi- 

 nation has seemed less and less. By far the greatest quantity of the 

 excrementitious carbon dioxide in the blood is extracted by the removal 

 of atmospheric pressure in the most carefully prepared apparatus. 



The quantity of carbon dioxide varies considerably in different parts 

 of the venous system. It is well known that the venous blood coming 

 from certain glands is dark during the intervals of secretion and is nearly 

 as red as arterial blood during secretion. In the venous blood from the 

 submaxillary gland of a dog, Bernard found 18.07 P er cent * carbon 

 dioxide during repose and 10.14 per cent during secretion. The blood 

 coming from the muscles is the darkest in the body and contains the 

 greatest quantity of carbon dioxide. The quantity of carbon dioxide, 

 also, is increased in the venous blood during digestion. 



These facts coincide with the views now held regarding the essential 

 processes of respiration. The blood going to the lungs contains carbon 

 dioxide and but a small proportion of oxygen. In the lungs carbon 

 dioxide is given off, appearing in the expired air, and the oxygen which 

 disappears from the air is carried away by the arterial blood. 



Nitrogen of the Blood. So far as is known, nitrogen has no impor- 

 tant office connected with respiration. There is sometimes a slight ex- 

 halation of this gas by the lungs, and analyses have demonstrated its 



