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. 



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. 1 



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

 and combined with bases. The quantity 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 their functional activ- 

 ity. In the venous blood from the submaxillary 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 ve- 

 nous 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 arte- 

 rial and venous blood varies considerably under different conditions of the system and 

 that it is variable in the blood of different veins, we rnay take the following, which we 

 quote from Bert, as the average results obtained by the most recent German observers: 



Oxygen. Carbonic Acid, Carbonic Acid, Carbonic Acid, Nitrogen. Total gas 



disengaged in combi- total. in volume 



by a vacuum. nation. per 100. 



"Arterial blood.. 15'03 27'99 1'15 29'14 TOO 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 blcod ; 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. 



"If we compare the venous blood of the right side of the heart with the arterial 

 blood of the left side, we find that the latter is richer in oxygen and poorer in carbonic 

 acid. In examining this more closely, we see that the difference in the oxygen is greater 

 than in the carbonic acid ; this being in accordance with the well-known fact that ani- 

 mals absorb more oxygen than is equivalent to the carbonic acid exhaled." 



These facts coincide with the views which are now held regarding the essential pro- 

 cesses of respiration. The blood going to the lungs contains carbonic acid and but a small 

 proportion of oxygen. In the lungs, carbonic acid is given off, appearing in the expired 

 air, and the oxygen which disappears from the air is carried away by the arterial blood. 



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

 summer of 1861. 



