EFFECTS OF RESPIRATION ON THE AIR. 525 



blood also contain nitrogen as well as carbonic acid, this also will pass out, to 

 be replaced by the oxygen of the air. Thus, there will be a continual exosmose 

 of carbonic acid and nitrogen, and a continual endosmose of oxygen and nitro- 

 gen.' The exhalation and absorption of Nitrogen appear usually to balance each 

 other, so that the amount of this gas in the respired air undergoes little change ; 

 a slight increase in the Nitrogen of the expired air being the alteration most 

 constantly noticed. But the case is different in regard to the exchange of Car- 

 bonic acid and Oxygen. According to the law of "mutual diffusion " of gases, 

 the volume of Oxygen that is taken in, should exceed that of the Carbonic acid 

 which passes out, in the proportion of 1174 to 1000 ; and it has been attempted 

 by Valentin and Brunner 1 to show, that, if a reasonable allowance be made for 

 accidental causes of disturbance, this is the actual proportion between the Oxygen 

 absorbed and the Carbonic acid given out, as indicated by experiment. Such, 

 however, cannot be the case, since the departures are too wide to be accounted 

 for on this hypothesis. Still there appears to the Author no adequate reason 

 for doubting that the process of exchange is mainly effected by the force of " mu- 

 tual diffusion " the result of its action, however, being determined by a great 

 number of modifying conditions ; so that the formula which expresses the law 

 of its action in those simplest cases, in which the result is determined solely by 

 the tendency to mutual penetration between gases on the opposite sides of a 

 porous septum that affords them free passage, can scarcely hold good when the 

 septum is a moist animal membrane, through which these gases pass with very 

 different degrees of facility, and when one side of it is in contact with the liquid, 

 through which they are diffusible with different degrees of readiness. 



563. The recent experiments of MM. Regnault and Reiset 3 appear to have 

 furnished the solution of the wide differences in the estimates which various 

 experimenters have given, as to the relative amount of Oxygen absorbed and of 

 Carbonic acid exhaled; by showing that it depends not, as Dulong and Des- 

 pretz supposed, upon the ordinary regimen of the animal (the proportion of 

 oxygen absorbed being much larger in Carnivora than in Herbivora) but upon 

 the nature of the aliment on which the animal is fed at the time of the experi- 

 ment. Animals fed on flesh absorb much more oxygen in proportion, than those 

 fed on a vegetable diet ; thus in a dog exclusively nourished on flesh, the pro- 

 portion of oxygen absorbed, to 100 parts of carbonic acid exhaled, was 134.3, or 

 much above that which the law of mutual diffusion would indicate ; whilst in a 

 rabbit fed exclusively upon vegetable food, the proportion of oxygen absorbed 

 was only 109.34 to 100 parts of carbonic acid exhaled, or less than the calculated 

 amount. The difference between the relative proportions of surplus Oxygen, in 

 the same animal, under opposite circumstances, was found to be as much as 

 62 : 104. These experimenters further ascertained that, when an animal is 

 kept fasting, the relation between the Oxygen absorbed and the Carbonic acid 

 exhaled is nearly the same as when the animal is fed on flesh j the reason ap- 

 parently being, that in the former case the animal's respiration is kept up at the 

 expense of the constituents of its own body, which corresponds with animal 

 food in their composition. There can be no doubt that, on the whole, a con- 

 siderable surplus of oxygen is absorbed into the system ; and it appears pro- 

 bable that a part of this additional oxygen is made to combine with hydrogen 

 furnished by the food or by the disintegration of the tissues, the water thus 

 generated forming part of that exhaled from the lungs ; whilst another part will 

 be applied to the oxidation of the Sulphur and Phosphorus, which are taken in 

 as such in the food, and which, after forming part of the solid tissues, are ex- 

 creted in the condition of sulphuric and phosphoric acids, chiefly through the 



1 Valentin's " Lehrbuch de Physiologic," band i. pp. 507-580. 



2 " Annales de Chimie et de Physique," 1849. 



