xi EESPIEATOKY EXCHANGES 375 



animal breathes pure oxygen or a mixture of fifteen parts nitrogen 

 and one of oxygen ; that during respiration the nitrogen does not 

 sensibly increase nor diminish, and may without injury be 

 substituted for hydrogen, which also behaves as an indifferent gas ; 

 that during digestion and the muscular movements the intensity 

 of respiratory combustion increases ; that lastly, the consumption 

 of oxygen in man increases sensibly when the external temperature 

 is lowered. 



As regards the seat of respiratory combustion, Lavoisier was 

 less happy than in his previous researches, for he asserted with 

 Seguin that it took place in the lungs, where the oxygen of the 

 air encountered the combustible material, represented by a hydro- 

 carbonous fluid. This hypothesis, which makes the lungs the seat 

 of respiratory combustion, was open to grave objections. It was 

 observed that the temperature of the lungs is no higher than that 

 of the other internal organs, making it dubious whether heat could 

 spread thence to the rest of the body. Starting from this fact, 

 Lagrange (born at Turin, 1736 ; died 1813), one of the most 

 illustrious of mathematicians, was the first to rectify Lavoisier's 

 error. He maintained the hypothesis that only gas exchanges 

 take place in the lungs, in which the blood circulating through 

 them yields its carbonic acid to the air and absorbs oxygen from 

 it ; and that respiratory combustion is accomplished in every part 

 of the body to which the blood circulates. 



III. The earliest experimental proofs of the theory of internal 

 or tissue respiration, as foreshadowed by Lagrange, were given by 

 Lazzaro Spallanzani (1729-1799), who claims an important place 

 in the history of the chemistry of respiration. In a long series of 

 comparative studies on the respiration of a great number of 

 animals, terrestrial, aquatic, vertebrate, aud invertebrate, he 

 extended the doctrine of Lavoisier, proving that oxygen is in every 

 case essential to life, and that in all it is absorbed by the organs of 

 respiration (lungs, gills, trachea, skin) and carried to the circula- 

 tion, where it determines the vitality of the tissues by entering 

 into combination with them. 



Further, by ingenious experiments on snails he showed that 

 excretion of carbonic acid is independent of absorption of oxygen, 

 since it remains almost always constant, even when these creatures 

 are enclosed in tubes, plunged in a mercury bath, and filled either 

 with water that has been boiled and deprived of gases by the air- 

 pump, or with nitrogen or hydrogen. 



The Memorie su la respirazione is the posthumous work of the 

 Abbe* Spallanzani, and contains only a few of his observations. 

 After his death the protocols of his experiments were confided to 

 his friend the Genevese scientist and librarian, Jean Senebier, who 

 extracted from them the materials for a work entitled Rapport de 

 I'air avec les dtres organises (Geneva, 1807). This is a valuable 



