154 CHANGES OF AIR AND BLOOD IN RESPIRATION. 



air has been made more and more nearly perfect, the quantity of carbon 

 dioxide in combination 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 perfected 

 apparatus. 



According to Bernard, arterial blood, while an animal is fasting, contains 

 nine to eleven parts per hundred in volume of oxygen. In full digestion, the 

 proportion is raised to seventeen, eighteen or even twenty parts per hundred. 

 The proportion varies in different animals, being much greater, for example, 

 in birds than in mammals. The quantity of carbon dioxide is even more 

 variable than the quantity of oxygen. During digestion there are five to six 

 parts per hundred of carbon dioxide in the arterial blood. During the inter- 

 vals of digestion this quantity is reduced to almost nothing ; and after fasting 

 for twenty-four hours, frequently not a trace is to be discovered. 



The quantity of carbon dioxide varies considerably in different parts of 

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

 some glands is dark, during the intervals of secretion, and nearly as red as 

 arterial blood, during secretion. In the venous blood from the submaxillary 

 gland of a dog, Bernard found 18-07 per cent, of 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 is increased in the venous blood during diges- 

 tion ; and it is owing to this that the gas then exists in quantity in the arte- 

 rial blood. Bearing in mind the fact that the proportion of gases in the 

 arterial and venous blood varies considerably under different conditions of 

 the system and that it is variable in the blood of different veins, the following 

 general statement, taken from Bert (1870), may be accepted as representing the 

 average results obtained up to that time. The most recent results, particularly 

 those obtained by German observers, present no important variations from 

 this average : 



Carbon dioxide Carbon dioxide Total gas 



disengaged in combi- Carbon dioxide, in volume 



Oxygen, by a vacuum. nation. total. Nitrogen. per 100. 



"Arterial blood. 15-03 27-99 1-15 29-14 1-60 45-77 



Venous blood.. 8-17 31-27 2-38 33-65 1-37 43-19 



" If the blood coming from different parts of the body be now examined, 

 it is found that the blood of the hepatic veins is poorer in oxygen and 

 richer in carbon dioxide than the general venous blood ; that the blood of 

 the portal vein presents the same characters to a higher degree; that the 

 blood of the muscles in contraction presents the same relations as compared 

 with the blood of muscles in repose or paralyzed ; that, on the other hand, 

 the blood of the glands has more oxygen during their activity than during 

 their repose. 



" In comparing the venous blood of the right side of the heart with the 

 arterial blood of the left side, it is found that the latter is richer in oxygen 

 and poorer in carbon dioxide. In examining this more closely, it is seen that 



