OF THE CUTANEOUS FUNCTION. 53 



Of the Cutane&ua Function. 

 Note Z. 



I. Cutaneous Exhalation, or Insensible Transpiration. In transpiration there appears 

 to be two actions, a physical one consisting of the evaporation in the air of the fluid 

 parts of the body ; and a vital action, giving rise to an excrenientitial exhalation, of 

 which the skin is the organ. This view of the subject is much contended for by DP. 

 Edwards ; but we think he has refined in an unnecessary manner in explaining it. The 

 cutaneous exhalation is doubtless an organic function of which the skin is the organ : 

 but, we conceive, that the skin must first perform its office before the physical action 

 can take place to any considerable extent ; in short, that as transpiration is pel-formed, 

 the physical law operates, and that both go on, the latter as a consequence of the for- 

 mer, pari passu, until an increase of the transpiration on the one hand, and an uncom- 

 monly dry state of the atmosphere, on the other, give us different results. When tiie 

 former takes place we perceive the formation of sweat, or the transpiration becomes 

 sensible : when the latter exists, then the phenomenon, for which Dr. Edwards and 

 some others have argued, as constituting one of the actions into which this function 

 may be divided, really supervenes to some extent. Thus we have witnessed, during 

 the Harmattan wind, which occasionally blows on the West coast of Africa, and which 

 is remarkable fov its dry ness, evaporation going on so rapidly as to give rise to very 

 inconvenient sensations, and even to serious disorders of the pai'ts which are usually 

 exposed to the air. In this case the evaporation exceeds the mere solution of the 

 transpired fluid in the surrounding atmosphere; and the parts of the body which are 

 subjected to its operation, have a portion of the fluids sent to the surface carried off 

 by it, in addition to what is exhaled by the natural and organic action of the vessels of 

 the skin. 



The cutaneous exhalation contains a portion of the carbonic and lactic acids. 



II. Of the Sweat or Sensible Exhalation When we said, if the production of the ha- 

 litus or insensible transpiration from the skin exceed the evaporation of it in the atmos- 

 phere, sweat is formed, we stated the source of this fluid. It is, therefore, produced the 

 from same vessels as the insensible perspiration- But although this is the case, with re- 

 spect to their source, there is some difference between the nature or chemical constitu- 

 tion of the sensible and insensible cutaneous exhalations. The former is generally less 

 charged with carbonic acid than the former, but it abounds more with the salts usually 

 excreted from the system. 



A careful view of the functions of the skin throughout the different classes of animals, 

 leads us to conclude that it performs operations which hold an intermediate place be- 

 tween those of respiration and elimination, that it partakes of the character of a respi- 

 ratory and of an eliminating organ. 



1. It is a Respiratory Organ This is shown by the circumstance of this function be- 

 ing performed in the lower order of animals by the surface only; and by the gradation 

 observed from these up to the higher orders, and by the gradual perfection at which 

 the respiratory organ arrives in ascending the scale of animal creation. In the 

 higher animals the respiratory apparatus becomes more and more distinct, and the func- 

 tion depending upon it more and more limited to appropriate organs; however, the 

 same type which characterizes the lower orders, and is most remarkable in them, is still 

 preserved throughout the whole series of the animal scale, although it becomes gradu- 

 ally, and nearly, but not altogether lost. Thus in man, the lungs perform the chief re- 

 spiratory process ; but, even in him, the respiratory function of the skin is remarkable, 

 Carbonic acid gas is produced from the cutaneous surface, transpiration also takes place 

 there ; and this respiratory act of the skin becomes more or more remarkable under 

 circumstances which diminish or partially obstruct the respirator}' process of the lungs. 

 Thus we found that the quantity of carbonic acid gas, formed in the lungs in a given time 

 and in the same individual, was about one-third less in a hot climate than in a cold one ; 

 this was about the average result of our experiments: whilst we observed that the respira- 

 tory function of the skin, both as respects the quantity of the insensible transpiration and 



