794 SPECIAL PHYSIOLOGY. 



larity, and increased secretion. Suppression of the cutaneous exhala- 

 tion and excretion, is more or less dangerous, causing either local 

 internal congestion or inflammation, or general poisoning of the blood 

 and fever, from the retention of effete matters in the system. Hence 

 the ill effects of sudden cold, or chill to the surface, especially after 

 previous overheating of the body to the point of fatigue, and with the 

 accumulation of effete substances of waste in it. The chief use of this 

 copious exhalation of water from the skin, as will be explained in the 

 Section on Animal Heat, is that of regulating the temperature of the 

 body, under variations of external temperature. 



The mutual balance between the respective quantities of the renal 

 and cutaneous exhalations, under different physical conditions, chiefly 

 those relating to the temperature and hygrometric condition of the air, 

 is shown by the facts, that in cold weather the skin exhales less, and 

 the kidneys excrete more fluid, whilst in warm weather the skin elim- 

 inates more and the kidneys less. The skin is sometimes said to reg- 

 ulate the quantity of fluid given off by the kidneys, and the quantity 

 of fluid left in reserve in the blood, and the soft tissues generally ; but 

 the kidneys should rather be regarded as the true regulators in this 

 matter. The skin, and also the lungs, are exposed to external influ- 

 ences of temperature, and to the relative hygrometric state of the air, 

 which must affect the quantity of their exhalations ; but the kidneys, 

 being placed in uniform conditions, are sensitive self-acting regulators, 

 operating through stimulation of the vasi-motor nerves, which govern 

 the state of the arteries and vessels of the giomeruli, and determine 

 the supply of blood. In certain conditions, moreover, the renal and 

 cutaneous excretions, instead of being vicarious as to quantity, are 

 simultaneously increased or diminished. 



The office of the perspiration, in removing effete matter from the 

 blood, is, in the first place, evident from the composition of its solid 

 constituents, although these are comparatively scanty. Supposing 30 

 oz. of perspiration to be the daily quantity excreted, the amount of 

 urea and of other peculiar solids thus eliminated, would be about Jd 

 oz. ; whilst the daily quantity of solid urinary products amounts to 

 from 2 oz. to 3J oz. 



1 As an organ of excretion, however, the skin further eliminates 

 carbonic acid gas. The skin, indeed, is, to a slight extent, even 

 in Man, a respiratory membrane, giving off carbonic acid, and actu- 

 ally absorbing oxygen. The quantity of carbonic acid gas exhaled 

 by the comparatively dry cutaneous surface of the human body, is, 

 of course, relatively to that given off by the lungs, very much less, 

 and has been variously estimated at from ^ to ^ (Scharling), at 

 s l % (Scharling and Hannover), and at yj^ (Edward Smith), of that 

 given off by the proper respiratory organs, the lungs. It is stated 

 that in regard to the skin, a little more carbonic acid is given off than 

 oxygen is absorbed, which is the reverse of what happens in the lungs; 

 but the estimation of the quantity of oxygen absorbed is extremely 

 difficult. The same remark applies to the nitrogen, a minute trace of 

 which is said also to be taken up by the skin. The activity of this 

 cutaneous respiratory process, as it must be called, is considerably in- 



