HISTORICAL. 635 



method of artificial respiration by means of a bellows, and demon- 

 strated by sending a continuous stream of air through the lungs 

 that the respiratory movements of these organs are in themselves, 

 as a mechanical process, in no wise an essential feature of respiration. 

 John Mayow in 1688-1674 discovered that air is not a simple ele- 

 ment, but contains a definite substance necessary to life and to 

 combustion. He designated this substance as the nitro-aerian 

 vapor or nitrous particles, because he believed that the same 

 substance is present in condensed form, as it were, in common niter, 

 having found that combustion is possible even in a vacuum in the 

 presence of niter. 



In the eighteenth century, as is shown in the work of the great 

 physiologist, Haller, the theories of respiration were in many 

 respects in a most unsatisfactory state. The new facts that had 

 been discovered made the old views untenable, but were not in 

 themselves sufficient to explain clearly what actually takes place. 

 Such periods of uncertainty and dissatisfaction are frequent enough 

 in the history of science. In 1757 Joseph Black rediscovered carbon 

 dioxid, calling it fixed air, and showed that it is present in expired 

 air. A little later Priestly discovered and isolated oxygen and 

 nitrogen; but, under the influence of an erroneous view of combus- 

 tion that had been advanced by Stahl, was unable to give his 

 discoveries a clear and satisfactory application. The final step 

 in this progress was made by the wonderful work of Lavoisier 

 between the years 1771 and 1780. He made correct analyses of 

 air and of carbon dioxid, he explained combustion as an oxidation 

 with the formation of CO^ and H^O, he showed that in respiration 

 the same process occurs, and that the blood takes oxygen from 

 the air and gives back to it in expiration the carbon dioxid and 

 water formed by combustion within the body. He gave us the 

 essential facts in the modern theories of respiration and physio- 

 logical oxidations. 



After Lavoisier the chief positive advances that have been made 

 have been in reference to the condition of the gases in the blood. 

 By means of the gas-pump Magnus (1837) obtained these gases 

 quantitatively and thus procured data which, as Liebig showed, 

 demonstrate that the oxygen is held in the blood, not in simple 

 solution, but in some form of chemical combination, probably 

 with the red corpuscles. Finally it was shown by Stokes and 

 Hoppe-Seyler that the oxygen is held in definite chemical com- 

 bination with the hemoglobin. The nature of the combination of 

 the carbon dioxid in the blood is not yet entirely understood, while 

 the actual nature of physiological oxidations — that is, the part 

 taken by the oxygen in the chemical reactions of living matter — • 

 is one of the great problems of nutrition wliich may need many years 

 for solution. 



