ANALYSIS OF THE BLOOD FOR GASES. 159 



the results obtained by Magnus which were made by Gay-Lussac and Magendie, soon 

 after their publication, and more recently by Harley and others. 1 



Bernard's experiments were made chiefly on dogs and had special reference to the 

 proportion of oxygen in the blood. In two specimens taken from a dog in good con- 

 dition, a specimen of arterial blood, drawn from the vessels by a syringe and put in con- 

 tact with carbonic oxide without being exposed to the air, was found to contain 18*28 

 per cent., and a specimen of venous blood, taken in the same way, 8-42 per cent., in vol- 

 ume, of oxygen. The proportion of gases in the blood is found to vary very considerably 

 under different conditions of the system, particularly with reference to the digestive 

 process. The following are the general results of later observations, showing the differ- 

 ences and variations in the proportions of all the gases in arterial and venous blood. 



Arterial blood, while an animal is fasting, contains from nine to eleven parts per 

 hundred 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 carbonic acid is even more variable than the quantity of oxygen. 

 During digestion there are from five to six parts per hundred of free carbonic acid in the 

 arterial blood. During the intervals of digestion this quantity is reduced to almost noth- 

 ing; and, after fasting for twenty-four hours, frequently not a trace is to be discovered.* 



Venous blood always contains a large quantity of carbonic acid, both free in solution 

 and combined with bases. This quantity varies in different parts of the venous system 

 and bears a relation to the color of the blood. 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 their functional activity. In the venous blood from the submax- 

 illary gland of a dog, Bernard found 18'07 per cent, of carbonic acid 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 free carbonic acid. The quantity of free 

 carbonic acid is immensely increased in the venous blood during digestion. It is owing 

 to this fact that the gas then exists in quantity in the arterial 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 especially variable in the blood 

 of different veins, we may take the following, which we quote from Bert, as the average 

 results obtained by the most recent German observers : 



0. C0 3 C0 2 C0 3 N. Total gas 



disengaged in combi- total. in volume 



by a vacuum. nation. per 100. 



" Arterial blood .. 15'03 27'99 1-15 2914 1-60 45'77 



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



"If we now examine the blood coming from different parts of the body, we find that 

 the blood of the hepatic veins is poorer in oxygen and richer in carbonic acid 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. 



1 To Magnus belongs the credit of demonstrating the important fact that oxygen, carbonic acid, and nitrogen can 

 be extracted from the blood by removing the atmospheric pressure. Before his observations, Gmelin, Mitscherlich, 

 and Tiedemann placed venous blood in a tube over mercury in the receiver of an air-pump, and, by removing the press- 

 ure as far as possible, caused the mercury to descend. On admitting air into the receiver and restoring the press- 

 ure, the mercury ascended, with the blood, again filling the tube completely. From this they reasoned that there 

 was no free carbonic acid in the blood. By passing up a little acetic acid, carbonic acid was set free, which led them 

 to believe that all the carbonic acid was in combination. Magnus showed that the reason why other observers had 

 failed to extract gas by means of the air-pump was that the rarefaction of the air was not carried sufficiently far. 



2 These results are quoted from Bernard and were given in his lectures delivered at the College of France in the 

 summer of 1861. More recent observations by German physiologists have shown that Bernard's estimates of the 

 proportions of carbonic acid were much too low. 



