EFFECTS OF RESPIRATION ON THE AIR. 529 



tious matters which the blood may contain. Strong tea is said to have the same 

 effect (Prout, Vierordt). The quantity is also decreased by depressing affections 

 of the mind (Prout, Vierordt, and Scharling). 



i. Period of the Day. Independently of these variations, which have their 

 source in the condition of the individual, there is reason to believe that there is 

 a diurnal cycle of change in the quantity of carbonic acid exhaled, the maximum 

 being (cseteris paribus) before and after noon, and the minimum before and after 

 midnight. From the experiments of Scharling upon the Human subject, it 

 would appear that the average proportion exhaled by day to that exhaled by 

 night, is as 1J to 1 ; and this difference does not seem to be affected by sleep or 

 wakefulness. How far it is to be accounted for by other differences in the con- 

 dition of the system, it does not seem easy to determine. But it is pretty ob- 

 viously associated with a difference in the power of generating heat ; for accord- 

 ing to the observations of Chossat (CHAP, xin.), there is a like diurnal variation 

 in the temperature of Birds ; and most persons are conscious of a greater difficulty 

 in bearing exposure to cold between midnight and early morning, than at any 

 other period in the twenty-four hours. 



565. The aeration of the blood may take place, not only by means of the 

 Lungs, but also in some degree through the medium of the Cutaneous surface. 

 In some of the lower tribes of animals, indeed, this is a very important part of 

 their respiratory process : and even in certain Vertebrata, the cutaneous respira- 

 tion is capable of supporting life for a considerable time. This is especially the 

 case in the Batrachia, whose skin is soft, thin, and moist ; and the effect is here 

 the greater, since, from the small proportion of the blood that has passed through 

 the lungs, that which circulates through the system is very imperfectly arterial- 

 ized. By the experiments of Bischoff it was ascertained that, even after the 

 lungs of a Frog had been removed, a quarter of a cubic inch of carbonic acid 

 was exhaled from the skin, during eight hours. Experiments which have been 

 made on the Human subject leave no room for doubt, that a similar process is 

 effected through the medium of his general surface, although in a very inferior 

 degree , for by confining the body in a close chamber, into which the products 

 of cutaneous respiration could freely pass, whilst the pulmonary respiration was 

 measured by a distinct apparatus, Prof. Scharling 1 ascertained that the propor- 

 tion of carbonic acid given off by the Skin is from l-30th to l-60th of that 

 exhaled from the Lungs during the same period of time. Moreover, it has been 

 observed, not unfrequently, that the livid tint of the skin which supervenes in 

 Asphyxia, owing to the non-arterialization of the blood in the lungs, has given 

 place after death to the fresh hue of health, owing to the reddening of the blood 

 in the cutaneous capillaries by the action of the atmosphere upon them ] and it 

 does not seem improbable that, in cases of obstruction to the due action of the 

 lungs, the exhalation of carbonic acid through the skin may undergo a consider- 

 able increase ; for we find a similar disposition to vicarious action in other parts 

 of the excreting apparatus. Moreover, there is evidence that the interchange 

 of gases between the air and the blood, through the skin, has an important 

 share in keeping up the temperature of the body (CHAP, xm.) ; and we find the 

 temperature of the surface much elevated in many cases of pneumonia, phthisis, 

 &c., in which the lungs seem to perform their function very insufficiently. 



566. The total amount of Carbonic acid daily given off from the Skin and 

 Lungs may be estimated in another mode ; namely, by determining the total 

 amount of Carbon contained in the ingesta, and the amount excreted in other 

 ways, making allowance for the difference in weight (if any) of the body. In 

 this mode, Prof. Liebig came to the conclusion that the average amount of car- 

 bon exhaled by soldiers in barracks, was 13.9 oz (Hessian) or very nearly 14 oz. 



1 " Ann. der Chem. und Pharm.," 1846. 

 34 



