EFFECTS OF RESPIRATION ON THE AIR. 399 



action of carbonic acid or morphia; whilst they augment in si/e when they 

 are exposed to a highly oxidized medium, or when they are placed under 

 conditions in which the oxygen escapes with difficulty, as after the adminis- 

 tration of refrigerants, quinine, alcohol, and hydrocyanic acid. Whether 

 the carbonic acid is chiefly formed without or within the vessels, it is certain 

 that the amount developed bears a close relation in all parts of the body 

 with the energy with which cell growth and function take place, and with 

 the activity of the interstitial changes coincident with these processes ; the 

 blood, which has then become charged with this gas and poor in oxygen, is 

 conducted to the lungs, when the converse changes are effected, the Carbonic 

 acid diffusing through the vessel into the. air contained in the pulmonary 

 alveoli, and being replaced by oxygen. The precise steps of this change are 

 not certainly known. Wolff berg 1 has demonstrated that the tension of the 

 Carbonic acid in the alveoli of the lungs, and in the venous blood of the 

 pulmonary artery, is nearly the same, and it is not clear why it should diffuse 

 through the walls of the bloodvessels. From some cause or other its tension 

 in the blood must be raised as this traverses the pulmonary capillaries. 

 Robin and others have attributed this elevation of tension to the formation 

 of an acid pneumic acid, whilst others have regarded it as the effect of the 

 formation of oxy haemoglobin, the expulsion of the Carbonic acid being de- 

 pendent on the absorption of Oxygen. 



317. Much discussion has taken place with regard to the degree in which 

 the proportion of Nitrogen in the air is affected by Respiration. It seems 

 probable that the absorption and exhalation of this gas are continually taking 

 place ; but that the two amounts usually nearly balance each other. 2 On 

 the whole, however, there is adequate reason to believe that Nitrogen is ordi- 

 narily given off; this being the joint result of the analysis of the expired 

 air, and of the comparison of the amount of nitrogen given off in the other 

 excretions with that ingested as a constituent of the food. In some experi- 

 ments made by Reguault and Reiset, on the composition of the expired air 

 in various warm-blooded animals, they arrived at the following conclusions : 

 (1.) That warm-blooded animals subjected to their ordinary regimen exhale 

 nitrogen, but never in larger proportion than -^gth, and sometimes in less 

 than T 5 D th, of the oxygen consumed; (2.) That in a state of inanition, ani- 

 mals usually absorb nitrogen ; (3.) That animals whose usual diet has been 

 changed, usually absorb nitrogen until they are accustomed to their new food. 3 

 -Voit,* in experiments on pigeons extending over 124 days, found that little 

 or no nitrogen is eliminated by the lungs in these animals, since the amount 

 contained in the urine and fbeces was equal to within 2.3 per cent, of that 

 ingested. This result is in marked contrast to that obtained by Boussiu- 

 gault, who found a deficit of 35 per cent, of nitrogen in the faeces and urine 

 when compared with that contained in the food. From Seegen's researches 

 on dogs, it appears that although generally the greater part of the nitrogen 

 is eliminated as urea, under certain circumstances, a large portion (one-half) 

 may be discharged by other channels, a portion probably escaping by the 

 lungs. Barral estimated that the amount of nitrogen which (being other- 

 wise unaccounted for) must be considered to have passed off by the lungs 



1 Wolffberg, Ucber die Athmung der Lunge, Pfliiger's Arehiv, Ed. vi, 1872, p. 

 23; Strassburgh, Die Topog. der Gasspannungen im Thierischen Organismus, in 

 idem, p. 65. 



2 For the considerations winch render this probable, see especially Dr. W. F. Ed- 

 wards, On the Influence of Physical Agents on Life, part, iv, chap, xvi, sect. 2, 3. 



3 Ann. de Chim. et de Pays., 18J9 ; and Mem. de Chiin. Agric., 18-34, p. 31. 



4 Henle and Meissner's Bericht, 1862, p. 342, and 1806, p. 390. 



5 Wiener Sitzungsberichte, 1867, Bd. Iv, March. 



