ADVANCED EXPERIMENTAL PHYSIOLOGY 141 



during the experiment oxygen and loses water and carbon dioxide. 

 The ratio CO a grms.32 CO, by volume =re . nt 



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 ten minutes, and was active. 



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

 103-116 decimgrms. carbon dioxide per ten 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 XXIV 



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 pump introduced by Leonard Hill. For other 

 methods see The Respiratory Function of the Blood, by J. Barcroft. 



The pump consists of a mercury reservoir A, which is connected 

 with a second reservoir B by means of pressure tubing. The con- 

 nection is surrounded by a mercury cup. The upper end of B is 

 closed by a three-way tap fitted with mercury cups. By means of 

 this tap B can be put in connection with either the tube E leading 

 to the blood-receiver F, or with the tube C leading to the eudiometer 

 H. The blood-receiver F is constructed of three bulbs, so as to 

 prevent the blood frothing over into B during the extraction of the 



