474 THE RESPIRATORY EXCHANGE 



search after the connection between the " breath of life " and 

 the soul led him to this important discovery and to the stake. 

 Not only did Servetus clearly describe the passage of the blood 

 from the right ventricle through the pulmonary artery, the lungs, 

 and the pulmonary veins into the left side of the heart, but he 

 pointed out that the bright colour was given to the blood by the 

 lungs, and not, as Galen had taught, by the heart. Although 

 the complete circulation of the blood was discovered by Harvey 

 before the year 1628, the real meaning of the pulmonary circula- 

 tion escaped him ; he thought that the function of the lungs was 

 to cool the blood. The fundamental knowledge of the circula- 

 tion was completed when Malpighi, about the year 1661, discovered 

 the alveoli of the lungs and saw the blood flowing through the 

 capillaries of a frog's lung. 



Further advance in the study of .respiration required the know- 

 ledge of physics and chemistry. This was soon forthcoming. 

 Boyle in 1666 showed by numerous experiments with the air-pump 

 that a supply of air was essential to both animal and vegetable 

 life, and he expressed the opinion that " the depuration of the 

 blood was one of the ordinary and principal uses of respiration." 

 A year or two earlier Fracassati had noticed that the lower layer 

 of a clot of blood was much darker in colour than the upper layer, 

 but lost its venous colour and became florid red when it was exposed 

 to the air. A similar aeration of the blood was effected by the 

 respiratory movements, the object of which was not, as some 

 physicians taught, to maintain the circulation of the blood, but 

 to ventilate the lungs with air. This important fact was demon- 

 strated by Hook to the Fellows of the Royal Society at one of 

 their meetings in 1667. The trachea of a dog was connected with 

 a pair of bellows, and the ribs and diaphragm were removed ; 

 the dog was seized with convulsions and appeared to be dying, 

 but revived when air was blown into its lungs. Small punctures 

 were now made into various parts of the lungs, and by means of 

 two pairs of bellows the lungs were kept fully distended with fresh 

 air ; the dog remained quiet and its heart beat regularly. The 

 circulation continued although there was no alternate expansion 

 and collapse of the lungs ; moreover, a further experiment showed 

 that even when the lungs were allowed to collapse the blood con- 

 tinued to circulate for some time. 



The real function of respiration was first set forth by Mayow ( 2 ) 



