RESPIRATION. 135 



The temperature of the blood varies considerably; but 

 the arterial stream is generally warmer than the venous. 

 The blood imparts heat to the air while passing through 

 the lungs, and consequently the contents of the right side 

 of the heart has a higher temperature than the contents 

 on 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 venous blood. There 

 evidently exists, on the part of these little bodies, an affin- 

 ity for this gas, and hence they have been called " carriers 

 of oxygen." It was long ago thought that blue blood was 

 a trait peculiar to persons of princely and royal descent, 

 and boastful allusions to the " sang azure" of kings and 

 nobles are quite often met with. Physiology, however, in- 

 forms us that blue blood flows in the veins of the low as 

 well as the high, and that so far from its presence indicat- 

 ing a mark of purity, it, in reality, represents the waste and 

 decay of the system. 



25. Amount of Respiratory Labor. During or- 

 dinary 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 



24. What do we learn by means of the spectroscope ? " Carriers of oxygen ?" 

 Blue blood in the system ? 



25. The amount of air that passes in and out of the lungs ? 



