EXPERIMENTATION AND PHYSIOLOGY 



The knowledge of the physiology of the res- 

 piratory system is founded on animal experi- 

 mentation. Galen early in the first century 

 observed that the diaphragm was the chief 

 muscle of respiration. He divided the spinal 

 cord of animals higher and higher and found 

 that as his operations ascended paralysis of 

 the intercostal muscles passed upwards. The 

 Hon. Robert Boyle (1670) experimented 

 upon rats, birds, frogs, fish, snakes, and in- 

 sects, and showed that atmospheric air was 

 necessary for their existence, and that vitiated 

 air must be replaced by fresh air. Mayo pub- 

 lished experiments in 1668 and 1674 showing 

 that the respiration of mice diminished the 

 amount of air by seven per cent. A hundred 

 years later Joseph Priestley discovered oxygen. 

 He then experimented upon mice and showed 

 that by enclosing a green growing plant with 

 the mouse the plant restored to the air the gas 

 which the animal consumed, and thus estab- 

 lished a complementary relation between ani- 

 mal and vegetable life. 



This experiment of Priestley's was the be- 

 ginning of the knowledge which is now 

 prompting the preservation of the forests in 

 civilized countries. Man began then to realize 

 4 35 



Physiolo- 

 gy of res- 

 piration. 



