ELEMENTARY EXPERIMENTAL PHYSIOLOGY 187 



by soda lime in M and sulphuric acid pumice in N. The amounts of 

 water and carbon dioxide given off in 15 minutes are determined by 

 the increase in weight of AB and CD respectively. The amount of 

 oxygen absorbed is found by subtracting the loss in weight of the 

 animal weighed in the chamber from the total loss of carbon dioxide 

 and water, for the animal absorbs during the experiment oxygen and 

 loses water and carbon dioxide. 



, CO grms. 32 C0 by volume 



The ratio -7^-- x = 2 , J } = respiratory quotient. 



O 2 grms. 44 O 2 by volume 



The effect of external temperature upon the respiratory exchange 

 may be studied with this apparatus. 



EXAMPLE. The beaker containing a full-grown mouse was placed 

 in a water-bath at 9'5 C. ; the mouse gave off from 250-315 decimgrms. 

 of carbon dioxide per 10 minutes, and was active. 



When the temperature of the bath was 30 C. the mouse gave off 

 103-116 decimgrms. carbon dioxide per 10 minutes, and was quiet. The 

 rectal temperature of the animal scarcely varied during the experiment. 

 Mammals born in a helpless condition, naked and blind, such as rats 

 and rabbits, behave like cold-blooded animals, and are unable to 

 compensate for low external temperature by increased metabolism ; the 

 output of carbon dioxide sinks as their body temperature falls. 



CHAPTER XLIX. 

 THE CHEMISTRY OF RESPIRATION. THE GASES OF THE BLOOD. 



IN a former chapter experiments were given to prove that the air 

 which is taken into the lungs loses a portion of its oxygen and gains 

 carbon dioxide; these changes correspond to differences in the gaseous 

 contents of the blood; the venous blood loses carbon dioxide and gains 

 oxygen in passing through the lungs, and thus becomes arterial. 

 Analysis shows that blood contains about 60 volumes per cent, of gas, 

 thus 100 volumes of arterial blood will yield 20 volumes of oxygen, 40 

 of carbon dioxide, and about 1 of nitrogen ; 100 volumes of venous 

 blood will yield 12 volumes of oxygen, 48 of carbon dioxide, and 1 of 

 nitrogen. 



Extraction and Analysis of the Gases of the Blood. There are 

 many forms of pump for the extraction of the gases of the blood ; the 

 general principle is the exposure of the blood to a barometric vacuum. 

 It will be sufficient for the student to work with the simple form of 



