194 INTERNAL RESPIRATION. 



chamber. It is less satisfactory to leave tlie 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 ascertained by enclosing it in an air-tight vessel (Rohrig) similar to that used for 

 the arm in the plethysmograph ( 101). 



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

 weight, which is greater than the loss by the lungs, in the ratio of 3 : 2. Only 10 

 grammes 150 grains, or it maybe 3*9 grammes 60 grains, of the entire loss are 

 due to the C0 2 given off by the skin. The remainder of the excretion from the 

 skin is due to water [l-2 ft) daily] containing a few salts in solution. When the 

 surrounding temperature is raised, the C0 2 is increased, in fact it may be doubled ; 

 violent muscular exercise has the same effect. 



Absorbed. The O taken up by the skin is either equal to, or slightly less 

 than, the C0 2 given off. As the C0 2 excreted by the skin is only ^-q- of that ex- 

 creted by the lungs, while the O taken in = yl^ 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, but 

 from other causes ( 225). 



In animals with a thin moist epidermis (frog) the exchange of gases is much greater, and in 

 them the skin so far supports the lungs in their function, and may even partly replace them 

 functionally. In mammals with thick dry cutaneous appendages, the exchange of gases is, 

 again, much less than in man. 



132. INTERNAL RESPIRATION. Where C0 2 is formed. By the term 

 " internal respiration " is understood the exchange of gases between the capillaries 

 of the systemic circulation and the tissues of the organs of the body. As organic 

 constituents of the tissues, during their activity, undergo gradual oxidation, and 

 form, amongst other products, C0 2 ; we may assume (1) that the chief focus for 

 the absorption of O and the formation of C0 2 is to be sought for within the 

 tissues themselves. That the O from the blood in the capillaries rapidly penetrates 

 or diffuses into the tissues, is shown by the fact that the blood in the capillaries 

 rapidly loses O and gains C0 2 , while blood containing O, and kept warm out- 

 side the body, changes very slowly and incompletely. If portions of fresh tissues 

 be placed in defibrinated blood containing O, then the O rapidly disappears. 

 Frogs deprived of their blood exhibit an exchange of gases almost as great as 

 normal. This shows that the exchange of gases must take place in the tissues 

 themselves. If the chief oxidations took place in the blood and not in the tissues, 

 then, during suffocation, when O is excluded, the substances which use up O, i.e., 

 those substances which act as reducing agents, ought to accumulate in the blood. 

 But this is not the case, for the blood of asphyxiated animals contains mere traces 

 of reducing materials (PJlilger). It is difficult to say how the O is absorbed by the 

 tissues, and what becomes of it immediately it comes in contact with the living 

 elements of the tissues. Perhaps it is temporarily stored up, or it may form certain 

 intermediate less oxidised compounds. This may be followed by a period of rapid 

 formation and excretion of C0 2 . On this supposition, it is evident that the absorp- 

 tion of O and the excretion of C0 need not occur to the same extent, so that the 

 amount of C0 2 given off at any period is not necessarily an index of the amount of 

 O absorbed during the same period (127). 



[There are two views as to where the C0 2 is formed as the blood passes through 

 the tissues. One view is that the seat of oxidation is in the blood itself, and the 

 other is that it is formed in the tissues. If we knew the tension of the gases in 

 the tissues, the problem would be easily solved, but we can only arrive at a know^ 

 ledge of this subject indirectly, in the following ways] : . 



C0 2 in Cavities. That the C0 2 is formed in the tissues, is supported by the fact that the 

 amount of C0 2 in the fluids of the cavities of the body is greater than the C0 2 in the blood of 

 the capillaries. The tension of C0 2 in 



