464 RESPIRATION. 



blood. As far as we know, no analyses of the human blood 

 have yet been made by his method. In two specimens taken 

 from a dog in good condition, a specimen of arterial blood, 

 drawn from the vessels by a syringe and put in contact 

 witli 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 volume, of 

 oxygen. 1 The proportion of gases in the blood is found to 

 vary very considerably under different conditions of the sys- 

 tem, particularly with reference to the digestive process. 

 The following are the general results of later observations, 

 showing the differences and variations in the proportions of 

 all the gases, in arterial and venous blood. 2 



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 quan- 

 tity is reduced to almost nothing ; and after fasting for twenty- 

 four hours, frequently not a trace is to le discovered. 



Venous Blood always contains a large quantity of car- 

 bonic acid, both free in solution, and combined in the form 

 of carbonates and bicarbonates. This quantity varies in dif- 

 ferent 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 sub-max- 



1 Loc. cit., p. 367. 



2 These results were given in a course of lectures which we had the privilege 

 of hearing at the College of France in the summer of 1861, and which have not 

 yet been published. 



