264 CUTANEOUS RESPIRATION. 



circulation, the oxyheemoglobin of the blood comes into relation with 

 tissues poor in 0; the oxyhaemoglobin is dissociated, the is supplied to 

 the tissues, and the blood freed from this 0, returns to the right heart, 

 and passes to the lungs, where it takes up new 0. 



The blood whilst circulating meets with most C0 2 in the tissues; 

 the high partial pressure of the C0 2 in the tissues causes the C0 2 to 

 unite with certain constituents in the blood so as to form chemical 

 compounds, which carry the C0 2 from the tissues to the lungs. In 

 the air of the lungs, however, the partial pressure of the C0 2 is very 

 low, dissociation of these chemical compounds occurs under the low 

 partial pressure, and the C0 2 passes into the air-cells of the lung, from 

 which it is expelled during expiration. It is evident that the giving 

 up of from the blood to the tissues, and the absorption of C0 2 from 

 the tissues, go on side by side and take place simultaneously, while in 

 the lungs the reverse processes occur also simultaneously. 



131. Cutaneous Respiration. 



Methods. If a man or an animal be placed in the chamber of a respiratory 

 apparatus (Scharling's, or v. Pettenkofer's), and if tubes be so arranged that the 

 respiratory gases do not enter the chamber, of course we obtain only the 

 "perspiration" of the skin in the chamber. It is less satisfactory to leave the 

 head of the person outside the chamber, while the neck is fixed air-tight in the wall 

 of the chamber. The extent of the cutaneous respiration of a limb may be ascer- 

 tained by enclosing it in an air-tight vessel (RiJhrig) similar to that used for the 

 arm in the plethysmograph (p. 198). 



Loss by Skin. A healthy man loses by the skin, in 24 hours, ^ T of 

 his body-weight (S6guin), which is greater than the loss by the lungs, 

 in the ratio of 3 : 2 (Valentin, 1843). Only 10 grammes 150 grains 

 (Scharling), or it may be 3'9 grammes 60 grains (Aubert), of the 

 entire loss is due to the C0 2 given off by the skin. The remainder of 

 the excretion from the skin is due to water, containing a few salts in 

 solution. When the surrounding temperature is raised, the C0 2 is 

 increased (Gerlach), in fact it may be doubled (Aubert) ; violent 

 muscular exercise has the same effect. 



Absorbed. The taken up by the skin is either equal to 

 (Regnault and Keiset), or slightly less than, the C0 2 given off. As the 

 C0 2 excreted by the skin is only f 3- of that excreted by the lungs, 

 while the taken in = -^ of that taken in by the lungs, it is evident 

 that the respiratory activity of the skin is very slight. Animals whose skin 

 has been covered by an impermeable varnish die not from suffocation, 

 tut from other causes. (See Artificial Diminution of Temperature.) 



