CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 731 



the amount of oxygen consumed is about equal in volume to that 

 of the carbonic acid given off, but some observers make it rather 

 less. It may be doubted, however, whether the carbonic acid conies 

 direct from the blood; it may come from decompositions taking 

 place in the sweat, of carbonates for instance. Similarly the oxygen 

 which disappears may be simply used in oxidizing some of the 

 constituents of the sweat. It is evident that the loss which the 

 body suffers through the skin consists, besides a small quantity of 

 sodium chloride, chiefly of water. 



When an animal, a rabbit for instance, is covered over with an 

 impermeable varnish such as gelatin, so that all exit or entrance 

 of gases or liquids by the skin is prevented, death shortly ensues. 

 It follows from what has just been said that this result cannot be 

 due, as was once thought, to arrest of cutaneous respiration. And 

 indeed the symptoms are rather of some kind of poisoning, possibly 

 caused by the retention within or reabsorption into the blood of 

 some of the constituents of the sweat, or by the products of some 

 abnormal metabolism. A marked symptom is the very great fall 

 of temperature, which however seems to be the result not of 

 diminished production of heat, but of an increase of the discharge 

 of heat from the surface ; owing to the dilated condition of the 

 cutaneous vessels caused by the application of varnish the loss of 

 heat through the skin is abnormally large, even though the varnish 

 may not be a good conductor. The animal may be restored, or at all 

 events its life may be prolonged with abatement of the symptoms, 

 if the great loss of heat which is evidently taking place be pre- 

 vented by covering the body thickly with cotton-wool, or keeping 

 it in a warm atmosphere. 



440. Absorption by the skin. Although under normal circum- 

 stances the skin serves only as a channel of loss to the body, it has 

 been maintained that it may, under particular circumstances, be a 

 means of gain ; and the little which we have to say on this matter 

 may perhaps be said here. Cases are on record where bodies are 

 said to have gained in weight by immersion in a bath, or by 

 exposure to a moist atmosphere during a given period, in which 

 no food or drink was taken, or to have gained more than the 

 weight of the food or drink taken ; the gain in such cases must 

 have been due to the absorption of water by the skin. Direct 

 experiments, however, throw doubt on these statements, for they 

 shew that under ordinary circumstances such a gain by the skin is 

 slight, being apparently due to mere inhibition of water by the 

 upper layers of the epidermis. 



Absorption of various substances takes place very readily by 

 abraded surfaces where the dermis is laid bare or covered only by 

 the lowest layers of epidermis, but it has been debated whether 

 substances in aqueous solution can be absorbed by the skin when 

 the epidermis is intact, the evidence on this point being contra- 

 dictory. In the case of the skin of the frog an absorption of water 



472 



