CHAPTER XVII. 

 CHEMISTRY OF RESPIRATION. 



DURING life a constant exchange of gases takes place between the 

 animal body and the surrounding medium. Oxygen is inspired and 

 carbon dioxide expired. This exchange of gases, which is called respira- 

 tion, is brought about in man and vertebrates by the nutritive fluids, 

 blood and lymph, which circulate in the body and which are in constant 

 communication with the outer medium on one side and the tissue-elements 

 on the other. Such an exchange of gaseous constituents may take place 

 wherever the anatomical conditions offer no obstacle, and in man it may 

 go on in the intestinal tract, through the skin, and in the lungs. As 

 compared with the exchange of gas in the lungs, the exchange already 

 mentioned, which occurs in the intestine and through the skin, is very 

 insignificant. For this reason we will discuss in this chapter only the 

 exchange of gas between the blood and the air of the lungs on one side 

 and the blood and lymph and the tissues on the other. The first is often 

 designated as external respiration, and the other, internal respiration. 



I. THE GASES OF THE BLOOD. 



Since the pioneer investigations of MAGNUS and LOTHAR MEYER the 

 gases of the blood have formed the subject of repeated careful investiga- 

 tions by prominent experimenters, among whom must be mentioned first 

 C. LUDWIG and his pupils and E. PFLUGER and his school and C. BOHR. 

 By these investigations not only has science been enriched by a mass of 

 facts, but also the methods themselves have been made more perfect 

 and accurate. In regard to these methods, as also in regard to the laws 

 of the absorption of gases by liquids, dissociation, and related questions, 

 the reader is referred to text-books on physiology, on physics, and on 

 gasometric analysis. 



The gases occurring in blood under physiological conditions are 

 oxygen, carbon dioxide and nitrogen, and traces of argon, and perhaps 

 also carbon monoxide. Traces of hydrogen and marsh-gas also some- 

 times occur. The nitrogen is found only in very small quantities, on an 

 average 1.2 vols. per cent. The quantity is here, as in all following 

 experiments, calculated for C. and 760 mm. pressure. The nitrogen 



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