CUTANEOUS RESPIRATION. 241 



thus evident that, as concerns the blood, the giving up of oxygen and 

 the absorption of carbon dioxid in the tissues, and, conversely, the 

 absorption of oxygen and the giving up of carbon dioxid in the lungs, 

 are processes that take place simultaneously. 



CUTANEOUS RESPIRATION. 



Method. If a human being or an animal is placed in the chamber of a respira- 

 tion-apparatus (such as Scharling's or v. Pettenkofer's) , and the gases passing to 

 and from the lungs are conducted through a respiratory tube, so that none of 

 the gaseous interchange of the lungs enters the chamber, but only the transpiration 

 of the skin, information can thus be obtained concerning the cutaneous respira- 

 tion. The procedure of leaving the whole head of the subject outside the chamber, 

 the neck being fixed air-tight in its wall, is less correct. The cutaneous respiration 

 of a circumscribed part of the body for instance, of an extremity -may be studied 

 by enclosing the part in an air-tight cylinder similar to that used for the arm in 

 employing the plethysmograph. 



In twenty-four hours a healthy man loses through his skin which 

 contains the respiratory organ in the moist sweat-glands, richly supplied 

 with blood-vessels QT of his entire body- weight, which is greater 

 than the loss through the lungs, since it bears a ratio to the latter of 

 3:2. Of this large loss of weight only from 8 to 10 grams are referable 

 to the carbon dioxid given off. The remainder is comprised in the 

 evaporation of water. Elevation of the surrounding temperature is 

 attended with an increase in the amount of carbon dioxid given off. 

 The excretion at between 29 and 33 C. amounts to 8 grams in twenty- 

 four hours; above 33 C. it is 20 grams (sweating begins at this 

 point); and at 38.4 C. the amount is 27.5 grams. Active muscular 

 exercise likewise produces an increased excretion. 



Absorption of oxygen by the skin has also been demonstrated, the 

 amount absorbed being either equal to the volume of carbon dioxid 

 given off, or a little less. 



As the excretion of carbon dioxid by the skin is only about -^ 

 of that by the lungs, and as the absorption of oxygen is only about T fo of 

 that by the lungs, it is evident that the respiratory activity of the skin 

 is in any event but slight. It is uncertain whether or not the skin gives 

 off gaseous nitrogen or ammonia. According to Funke the skin secretes 

 hourly 0.0824 gram of soluble nitrogen, this quantity being increased 

 in the presence of renal disease. 



According to Rohrig, the excretion of carbon dioxid and of water exhibits 

 certain daily variations. It is increased during digestion, after the application of 

 cutaneous irritants, in the presence of obstruction to pulmonary respiration, of 

 hyperemia of the skin, and when the blood contains an increased number of 

 erythrocytes. 



In warm-blooded animals, with thick, dry epidermoid structures, the cuta- 

 neous interchange of gases is still less than it is in man. In frogs and other am- 

 phibia, with a constantly moist skin, cutaneous respiration becomes highly impor- 

 tant. The skin here supplies from two-thirds to three-fourths of the total quantity 

 of carbon dioxid excreted, and in hibernating frogs the proportion is still greater. 

 The skin is, therefore,, a more important respiratory organ than the lungs. Im- 

 mersion in oil will, consequently, kill these animals more readily than will hgatic 

 the lungs. 



INTERNAL RESPIRATION OR TISSUE-RESPIRATION. 



The terms internal respiration and tissue-respiration are used to desig- 

 nate the interchange of gases between the capillaries of the greater cir- 

 16 



