CONNECTION BETWEEN BLOOD AND GASES 521 



is not quite exact, for the experiments made by Bohr and 

 Henriques show that blood absorbs a little more nitrogen ; about 

 1-2 volumes per cent, are the total amount found in both venous 

 and arterial blood. A further important point in the considera- 

 tion of the variations in the carbon dioxide and oxygen is the 

 time which elapses between the removal of the blood from the 

 animal and the completion of the extraction of the gases. Pniiger 

 found by comparative experiments with a large vacuum that the 

 ordinary methods for the extraction of gases give results which 

 are for the oxygen too low, for the carbon dioxide too high. This 

 is due to the fact that the blood is a living tissue which consumes 

 oxygen and produces carbon dioxide ; owing to this cause blood 

 kept from contact with the air rapidly becomes darker in colour, 

 even when no putrefactive changes have occurred. 



In addition to oxygen, carbon dioxide, and nitrogen, there are in 

 blood traces of argon, carbon monoxide, hydrogen, and marsh-gas ; 

 the source of the first and second is probably the inspired air, for 

 small quantities of carbon monoxide are found in the air of large 

 cities, where a large consumption of coal and gas occurs ; the 

 fermentation produced by bacteria in the food of the alimentary 

 canal is to be regarded as the source of the hydrogen and marsh-gas. 



It is convenient to take the following figures as the average 

 values of the gases of the arterial and venous blood. 



Arterial blood Oxygen, 20 ; carbon dioxide, 43 ; nitrogen, 



1-2 volumes per cent. 

 Venous blood Oxygen, 1 2 ; carbon dioxide, 50 ; nitrogen, 



1-2 volumes per cent. 



The respiratory quotient obtained therefrom is -^- 2 = 5 - A = 0'87. 



U 9 o 'U 



The nature of the connection between the blood and its 

 gases must now be considered, for the blood is very complex, and 

 its gases are distributed in both plasma and corpuscles. A neces- 

 sary preliminary to the study of this question is a knowledge of 

 the principles which underlie the investigation of gases, whether 

 they be free, in solution, or in chemical combination. There are 

 certain well-known laws. Dalton's Law : In a mixture of several 

 gases which have no chemical action upon one another, the pressure 

 of the mixture is equal to the sum of the pressures of the different 

 gases, each being considered as alone occupying the total volume. 



