200 RESPIRATION 



blood imparts heat to the air while passing through the lungs, 

 and consequently the contents of the right side of the heart 

 have a higher temperature than the contents of the left side.* 



24. By means of the spectroscope, we learn that the change 

 of color in the blood has its seat in the corpuscles ; and that, 

 according as they retain oxygen, or release it, they present the 

 spectrum of arterial or of venous blood. There evidently 

 exists, on the part of these little bodies, an affinity for this gas, 

 and hence they have been called " carriers of oxygen." It was 

 long ago thought that blue blood was peculiar to persons of 

 princely or royal descent, and boastful allusions to the " sang 

 azure" of kings and nobles are often met with. Physiology, 

 however, informs us that blue blood flows in the veins of all 

 the low as well as the high and really indicates waste and decay. 



25. Respiration of Cells. The blood of the capillary arteries 

 coining from the lungs, where it has been supplied with oxygen, 

 passes through the tissues of all parts of the body as already 

 stated, and here each cell receives its necessary supply of oxy- 

 gen from the blood, and gives up in return carbon dioxide and 

 other waste matters, which are then carried through the veins 

 to the organs of excretion. 



26. Amount of Respiratory Labor. During ordinary calm 

 respiration, we breathe eighteen times in a minute ; and twenty 

 cubic inches of air pass in and out of the lungs with every 

 breath. This is equivalent to the use of three hundred and 

 sixty cubic inches, or more than ten pints of air each minute. 

 From this we calculate that the quantity of air which hourly 

 traverses the lungs is about thirteen cubic feet, or seventy-eight 

 gallons ; and daily, not less than three hundred cubic feet, or 

 nearly sixty barrels. 



27. Of this large volume of air five per cent, is absorbed in 

 its transit through the lungs. The loss thus sustained is almost 

 wholly of oxygen, and amounts to fifteen cubic feet daily. The 

 quantity of carbonic acid gas exhaled by the lungs during the 

 day is somewhat less, being twelve cubic feet. Under the in- 



24. What do we learn by means of the spectroscope ? 25. Respiration of cells ? 



26. Amount of air that passes in and out of the lungs ? 



27. Air absorbed in its transit through the lungs ? 



