THE BLOOD. 95 



amounts have significant variations, not only in the blood from 

 different blood-vessels, but also because many conditions, such as a 

 difference in the circulation, a different temperature, rest and ac- 

 tivity, cause a change. The arterial and venous blood show the 

 greatest difference in regard to the gases they contain. 



The amount of oxygen in the arterial blood of dogs is on an 

 average 22 vols. per cent (PFLUGER). In human blood SETSCHENOW 

 found about the same amount, namely, 21.6 vols. per cent. Lower 

 figures have been found for rabbit's or bird's blood, respectively 

 13.2$ and 10-15$ (WALTER, JOLYET). Venous blood has very vari- 

 able amounts of oxygen. LUDWIG and SCZELKOW found 6.8$ oxy- 

 gen in the venous blood of quiet muscles and a still smaller amount 

 in the venous blood of active muscles. Oxygen is entirely absent 

 from blood after asphyxiation, or only occurs as traces. The venous 

 blood of the glands seems, on the contrary, during secretion to be 

 richer in oxygen than ordinary venous blood. By summarizing a 

 great number of analyses by different experimenters, ZUNTZ has 

 calculated that the venous blood of the right side of the heart con- 

 tains on an average 7.15$ less oxygen than the arterial blood. 



The amount of carbon dioxide in the arterial blood of dogs is 

 30 to 40 vols. per cent (LUDWIG, SETSCHENOW, PFLUGER, P. BERT, 

 and others), most generally about 40$. SETSCHENOW found 40.3 

 vols. per cent in human arterial blood. The amount of carbon 

 dioxide in venous blood varies still more (LUDWIG, PFLUGER and 

 their pupils, P. BERT, MATHIEU and URBAHST, and others). Accord- 

 ing to the calculations of ZUNTZ the venous blood of the right side 

 of the heart contains about 8.2$ more carbon dioxide than the 

 arterial. The average amount may be put down as 48 vols. per cent. 

 HOLMGREN found indeed in blood after asphyxiation 69.21 vols. 

 per cent carbon dioxide. 



Oxygen is absorbed only to a small extent by the plasma or 

 serum, in which PFLUGER found but 0.26$. The greater part 

 or nearly all of the oxygen is loosely combined with the haemo- 

 globin in oxyhaemoglobin. The quantity of oxygen which is con- 

 tained in the blood of the dog corresponds closely to the quantity 

 which we would expect from the activity of the haemoglobin 

 to combine with oxygen, and also the quantity of haemoglobin in 

 Canine blood. It is difficult to ascertain how far the circulating 



