EFFECTS OF RESPIRATION 489 



It has been found that in the case of man, and probably therefore also 

 in the horse, climate materially affects the absorption of oxygen. Thus, 

 under ordinary conditions of respiratory activity in the hot climate of 

 Madras, a man absorbs in one month 177 lbs. of oxygen, in the drier air of 

 London or Brussels, 192 lbs., in the still drier atmosphere of St. Petersburg 

 or Barnaul in Tomsk, 199 lbs., and in the latter place in winter, when the 

 quantity of moisture in the air is at a minimum, as much as 218 lbs. 

 These differences in some measure account for the languor experienced in 

 hot climates, and for the briskness and great heat-producing power ex- 

 hibited by the body in cold climates. 



Air-changes in the Blood. — We may now enquire into the nature 

 of the changes that take place in the blood from the time that it leaves 

 the lungs in an aerated state, or in the condition of arterial blood, till 

 it is returned to the heart in a venous condition after having traversed 

 the various organs of the body. The results that have been obtained 

 by those chemists who are the best qualified to deal with this difficult 

 subject show that from 100 volumes of blood about 60 volumes of 

 gas can be abstracted. The gases consist of carbon dioxide, oxygen, 

 and a little nitrogen, the proportion differing considerably according 

 to whether arterial or venous blood is examined. In both kinds of 

 blood the carbon dioxide is in great excess. Thus in 100 volumes of 

 arterial blood there are: oxygen 20, nitrogen 1 to 2, carbon dioxide 40 

 volumes. In 100 volumes of venous blood there are: oxygen 8 to 10, 

 nitrogen 1 to 2, and carbon dioxide 46 volumes. The nitrogen may be 

 dismissed from consideration at once, for it is known that it presents no 

 special affinity for any of the constituents of the blood, that it is absorbed 

 as water would absorb it, and that its volume consequently remains un- 

 changed. It is different with the other two gases. The oxygen introduced 

 into the lungs by the process of inspiration rapidly diffuses through the 

 delicate walls of the air-cells and the blood-vessels around them, and at 

 once enters into a feeble chemical combination with the hsemogiobin con- 

 tained in the red blood corpuscles. By these it is distributed through the 

 system, and in less than ten seconds reaches the capillary vessels, where 

 the blood is brought into close relation but not in actual contact with the 

 tissues. These have a stronger affinity for oxygen than the haemoglobin of 

 the blood; it therefore leaves the red corpuscles, and, passing through the 

 thin walls of the blood and lymph vessels, finally attacks or is seized upon 

 by the tissues, muscle or nerve or gland, as the case may be. 



The quantity of carbon dioxide that is generated in the tissues, to be 

 taken up by the plasma of the blood and to be discharged from the body 

 at the lungs, is dependent upon many circumstances. To liberate the force 



