448 THE POPULAR SCIENCE MONTHLY. 







HOW ANIMALS BREATHE. 



By HERMAN L. FAIECHILD. 



A NIMAL COMBUSTION. Within every living organism there 

 -E- j- are two opposing forces. The " vital force," which produces all 

 the phenomena of life, holds the material elements in unstable rela- 

 tions against their will, so to speak and it is antagonized by the 

 natural chemical affinities of the elements, which tend to break down 

 the organic compounds and rearrange the elements in more stable 

 form. This decomposition takes place in some degree during the life 

 of every organism, and when life ends, or when the vital force ceases 

 to act, it rapidly destroys the structure. 



The waste matter resulting from this disintegration must be im- 

 mediately removed from the body of the living animal, otherwise it 

 clogs and poisons the system. The method of its accomplishment is 

 one of the most admirable functions of the animal economy. To re- 

 move the effete matter in the natural liquid or solid state would be 

 very exhausting ; consequently it is burned, and the gaseous products 

 of its union with oxygen are then easily carried away. Literally 

 speaking, this makes a furnace of the body of every animal ; and the 

 most pressing and ceaseless demand of the system is for oxygen to 

 support its fires. Respiration is hence an absorbing and excreting 

 process, whereby oxygen is received and carbonic acid and water re- 

 moved. It thus becomes a measure of the amount of combustion. 



In the "cold-blooded" animals respiration bears a direct propor- 

 tion to the activity and the heat of the body, as the former causes a 

 metamorphosis and waste of tissue, and the latter always aids decom- 

 position. The fact is one of common observation. It is well illus- 

 trated in the quickened breathing of a tired animal, and in the almost 

 entire suspension of respiration in the hibernating state. The respira- 

 tion of a " cold-blooded " creature is increased by artificial heat. In 



Fig. 1. Cobitis Fossilis. Tt swallows air-bnbblep which pass throngb the intestine, where the 

 mucous membrane takes up the oxygen for respiration. 



extremely hot weather frogs may have to leave the water entirely, and 

 fishes come to the surface to procure air. Reversely, frogs can be 

 kept for years in a state of suspended animation by a low temperature, 

 and revived by warming. Some low animals can survive freezing or 



