46 PHYSIOLOGICAL REMARKS. 



overwhelmed, and, as it were, drowned in its own blood. The heart 

 is nothing more than a double forcing-pump of most beautiful 

 construction, one half of which receives the blood from all parts 

 of the body, and forces it into the lungs (through the most 

 minute portions of which it passes), whilst the other half receives 

 this blood after it has passed through the lungs, and then forces it 

 into all parts of the body, supplying the wants of the nervous 

 system, the muscles, bones, skin, and also all the organs of 

 digestion, &c. ; and being itself composed of muscular substance. 

 The vessels or tubes conveying this blood are respectively called 

 arteries and veins, having intervening between their extremities a 

 network of vessels so minute as to be called capillaries from 

 capillus, a hair. 



In this rough enumeration of the various organs, we must next 

 consider the agency of the lungs, which has only lately been fully 

 understood. By the researches of modern physiologists, it is now 

 ascertained that these organs are chiefly intended to supply the 

 heat which is required for the performance of all healthy functions. 

 Without the lungs no warm-blooded animals could resist the cold 

 even of an English winter, when exposed to its action without 

 protection ; but, by their agency, such a temperature is preserved 

 as is required, and nothing in the animal economy is more beauti- 

 ful than this process. Now, this heat-maintaining power is owing 

 to the combination of the carbon and hydrogen in the blood with 

 the oxygen of the air, forming respectively carbonic acid and 

 water, and being effected in the lungs through the thin mem- 

 branous walls of the capillary vessels at the time of the circulation 



