Interchange of Pulmonary Gases in Respiration of Man. 213 



*' Contribution to the History of the Interchange of Pul- 

 monary Gases in the Respiration of Man." By WILLIAM 

 MARCET, M.D., F.R.S. Received June 9, Read June 16, 

 1892.* 



I had the honour of communicating a paper to the Royal Society 

 in June, 1891, embodying the results obtained from a first series of 

 inquiries on the interchange of pulmonary gases. The investigation 

 has been continued, and I have had the benefit of the assistance of 

 Mr. Gr. P. Darnell Smith, B.Sc., in the present work. I am greatly 

 indebted to Mr. Smith for many useful suggestions ; while our dis- 

 cussions have been fruitful on many occasions. 



The apparatus used for the estimation of carbonic acid and oxygen 

 has been fully described in my former paper, but, as the drawing of 

 the eudiometer employed could not be inserted in that communica- 

 tion, it is appended to this paper together with an explanation of 

 the construction of the instrument. 



The key to a method of investigation calculated to give correct 

 information on the interchange of the respiratory gases is to be found 

 in the means adopted for the determination of the volumes of air 

 inspired and expired. C. Speck in his experiments, inspired a 

 measured volume of air from a bell-jar, carefully balanced over a 

 water trough, and expired it into another, the volumes of air in- 

 spired and expired being thus determined by direct measurement. 

 Messrs. Hanriod and Richet used gas meters instead of bell- jars. In 

 my former inquiry, after trying how closely experiments with bell- 

 jars agreed with each other, it was found that the results obtained 

 were not sufficiently reliable to be used except in the form of means ; 

 on that account, the object was attained by calculation, assuming that 

 the volume of nitrogen in the air expired was exactly the same as 

 the volume of nitrogen in the air inspired ; consequently the volume 

 of nitrogen expired was proportional to the volume of air inspired. 



It has occurred to me that an objection to this means of deter- 

 mining the volume of air inspired might be raised on the ground 

 that it is unscientific to adopt a method of inquiry based on an 

 assumption, although the investigations of Regnault and Reiset have 

 apparently placed what I call an assumption on the footing of an 

 acknowledged fact. There was consequently a gap to fill up, as it 

 was necessary to ascertain whether nitrogen is either absorbed in the 

 blood or given out, or whether it takes no appreciable part in the 

 respiratory process; with this object, an experiment was made by 

 re-breathing a known volume of air in a bell- jar, and determining 

 afterwards the volume of nitrogen present in this air, but the 

 * Eeyised August, 1892. 



