RESPIRATION. 



the lungs, and carried out in the expired air. 

 If, then, we add an increased flow of blood 

 through the capillaries of the lungs to an in- 

 creased frequency of the respiratory move- 

 ments, as occurs in exercise, the interchange 

 between the oxygen of the air and the free 

 carbonic acid of the blood will be carried on 

 with greater activity. When, on the other 

 hand, the air is renewed in the lungs less fre- 

 quently than usual, as happens when the 

 respiratory movements are diminished in 

 number and in extent, the air in the deeper 

 parts of the lungs will contain less oxygen 

 and more carbonic acid than usual, and the 

 interchange between the oxygen of the atmo- 

 spheric air and the free carbonic acid of the 

 blood will proceed more slowly. When the 

 respirations are reduced to about one half of 

 their normal frequency, as occurs in the course 

 of some diseases, and after division of the 

 vagi nerves, the carbonic acid gas gradually 

 accumulates in the blood, less oxygen is ab- 

 sorbed, and the individual generally sooner or 

 later dies of asphyxia. When the quantity of 

 carbonic acid gas in the air-cells reaches a 

 certain amount, the evolution of this gas from 

 the blood will cease ; and when this is carried 

 still farther, there will be an absorption of a 

 part of the carbonic acid gas by the blood. 



The interchange between the nitrogen and 

 the other gases at the lungs is very small in 

 the normal condition of the respiration, but 

 there is every reason to believe that this is 

 regulated by circumstances similar to those 

 which determine the interchange of the oxygen 

 and carbonic acid. The nitrogen is much 

 less soluble in the blood than the oxygen and 

 carbonic acid, and we presume that its power 

 of permeating moist animal membranes is 

 much inferior to these gases, and that the 

 smaller quantity of it held in solution in the 

 blood may be in this manner explained. We 

 have already pointed out that, in the experi- 

 ments made to determine whether nitrogen is 

 absorbed or exhaled at the lungs, opposite 

 results have been obtained, but that the evi- 

 dence preponderates in favour of the opinion 

 that a small quantity of this gas is evolved 

 from the blood during respiration. By an 

 alteration of the usual relation between the 

 quantities of nitrogen present in the air and 

 in a free state in the blood, the evolution of 

 nitrogen from the blood may be increased or 

 suspended, or it may be absorbed by the blood 

 instead of being evolved by it. In a previous 

 part of this article we have referred to ex- 

 periments which prove that when animals 

 breathe oxygen or hydrogen gases, or a mix- 

 ture of both, azote is evolved in greater 

 quantity than usual from the blood in the 

 lungs; and that when they breathe azote 

 alone, part of this gas is absorbed at the 

 lungs. 



The exact condition in which the whole of 

 the oxygen absorbed at the lungs exists in 

 the blood, notwithstanding the light thrown 

 upon this point by recent researches, is still 

 not free from considerable difficulties. Pre- 

 vious to the experiments of Magnus upon the 



gases of the blood, already referred to, the 

 opinion of Le Grange and Hassenfratz, that 

 the greater part of the oxygen gas absorbed at 

 the lungs is dissolved in the blood and carried 

 along with it in that condition to the systemic 

 capillaries, was considered untenable by many 

 celebrated physiologists, the more especially 

 as the attempts to detect free oxygen in the 

 arterial blood had failed in all the more 

 trust-worthy experiments. Different opinions 

 as to the kind of chemical combination 

 formed by the oxygen in the arterial blood 

 have been entertained by those who believe 

 that the portion of this gas that disappears 

 from the inpired air does not unite with car- 

 bon in the lungs to form carbonic acid, and 

 that little or none of it is simply dissolved 

 in the arterial blood. In the greater number 

 of these hypotheses, however, the oxygen is 

 supposed to unite itself in whole or in part 

 to the red corpuscles, and especially to the 

 iron contained in these : and as the exact 

 state in which the metal exists in the red 

 corpuscles is still undetermined, this has given 

 rise to very different notions regarding the 

 changes effected upon it by the oxygen. 

 According to other views, the oxygen in 

 whole or in part is united chemically to some 

 of the other constituent parts of the arterial 

 blood, and from these it is again separated in 

 passing through the systemic capillaries, and 

 unites with carbon to form carbonic acid.* 



* We shall here very shortly notice a few of the 

 more recent theories of respiration, which proceed on 

 the supposition that the oxygen abstracted from the 

 inspired air is combined, in whole or in part, with 

 some of the constituents of the arterial blood. Gme- 

 lin, Tiedemann, and Mitscherlich (Zeitschrift fur 

 Physiologic, Band v.) supposed that the oxygen 

 absorbed at the lungs partly unites with carbon 

 and hydrogen to form carbonic acid and water 

 which are there exhaled, and partly with organic 

 substances in the blood to form acetic and lactic 

 acids : that these acids decompose some of the car- 

 bonates of soda brought to the lungs in the venous 

 blood, and that the carbonic acid thus set free is 

 also exhaled. The arterial blood in its course through 

 the tissues, more especially those of the kidneys and 

 skin, loses part of its acetic and lactic acids ; and 

 the soda with which they were combined, being set 

 free, unites with the carbonic acid formed during 

 the process of nutrition, and these carbonates are 

 again decomposed in the lungs in the manner de- 

 scribed. Dumas (Statique Chimique des Etres Or- 

 ganise's, pp. 43, 44, 3me edit.) believes that the 

 absorbed oxygen combines with certain matters of 

 the blood and forms lactic acid, the lactic acid com- 

 bines with soda to form lactate of soda, and this 

 latter salt, by a real combustion, is converted into 

 carbonate of soda, which is decomposed in its turn 

 in the lungs by a fresh portion of lactic acid. Liebig 

 (Organic Chemistry of Physiology and Pathology, 

 edited by Gregory, p. 265. 1841) supposes that car- 

 bonate of protoxide of iron exists in the red cor- 

 puscles of venous blood, and that in its passage 

 through the lungs, a large portion of the absorbed 

 oxygen unites with it, forms hydrated peroxide of 

 iron, and sets the carbonic acid free. Mulder (The 

 Chemistry of Vegetable and Animal Physiology, 

 translated by Fromberg, Part II. p. 337) affirms that 

 an alternate change into carbonate of the protoxide 

 of iron and peroxide of iron in respiration is impos- 

 sible, and maintains that the absorbed oxygen com- 

 bines with the proteine compounds of the blood and 

 forms oxy-proteine, which being conveyed by the 



