THE NATURE AND AMOUNT OF PERSPIRATION. 433 



the skin. In mammals and in man this cutaneous respiration is, by reason 

 of the thickness of the epidermis, restricted within very narrow limits ; and, 

 indeed, it has been questioned whether it can be spoken of at all as a true 

 respiration. When the body remains for some time in a closed chamber to 

 which the air passing in and out of the lungs has no access (as when the 

 body is enclosed in a large air-tight bag fitting tightly round the neck, or 

 where a tube in the trachea carries air to and from the lungs of an animal 

 placed in an air-tight box), it is found that the air in the chamber loses 

 oxygen and gains carbonic acid. The amount of carbonic acid which is thus 

 thrown off by the skin of an average man in twenty-four hours amounts to 

 about 10 grms., or according to some observers to (no more than) about 4 

 grms., increasing with a rise of temperature and being very markedly aug- 

 mented by bodily exercise. It is stated that the amount of oxygen con- 

 sumed 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 comes direct from the blood ; it may come from decom- 

 position 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 imper- 

 meable varnish, such as gelatin, so that all exit or entrance of gases or 

 liquids by the skin is prevented, death shortly ensues. This result cannot 

 be due, as once thought, to arrest of cutaneous respiration, seeing how insig- 

 nificant and doubtful is the gaseous interchange by the skin as compared 

 with that by the lungs. Nor are the symptoms at all those of asphyxia, but 

 rather of some kind of poisoning, marked by a very great fall of tempera- 

 ture, 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. The ani- 

 mal may be restored, or at all events its life may be prolonged with the 

 abatement of the symptoms, if the great loss of heat which is evidently 

 taking place be prevented by covering the body thickly with cotton-wool or 

 keeping it in a warm atmosphere. The symptoms have not as yet been 

 clearly analyzed, but they seem to be due in part to a pyrexia or fever pos- 

 sibly 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 meta- 

 bolism, and in part to a dilatation of the cutaneous vessels caused by the 

 application of varnish ; owing to the dilated condition of the cutaneous ves- 

 sels the loss of heat through the skin is abnormally large, even though the 

 varnish may not be a good conductor. 



368. Absorption by the skin. Although under normal circumstances 

 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 show that under ordinary circumstances 

 such a gain by the skin is slight, being apparently due to mere imbibition 

 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 



28 



