238 OF THE SEBACEOUS GLANDS. 



Such being the construction of the skin, we have next to speak of its 

 action. It discharges a double function : 1st, as an excreting, and, 2d, 

 as an absorbing organ. In this respect it has an analogy with the mu- 

 cous membrane, which, indeed, is a reflection or continuation of it. 



Of the excreting action of the skin. The skin permits water, saline 

 Different kinds an ^ fatty substances, to escape from it in quantities which 

 of perspiration, differ on different portions of its surface, the nature of the se- 

 cretions varying to meet local requirements. In the examination which 

 we are now entering upon, we shall speak of these substances and their 

 proportions in a general way, overlooking, for the time, the particular va- 

 riations. Yet that such variations exist is clear on the most superficial 

 observation. The sweat of the feet differs from that of the general sur- 

 face, as, again, does that of the arm-pits. 



It has been usual to distinguish the watery transudation into two por- 

 Quantityof tions, that which escapes from the perspiratory ducts, and 

 water through that passing through the surface of the cuticle. It has even 



the cuticle and , r . , J? - ,* i j i . e 



from the ducts been said that the true glandular secretion passing from the 

 compared. ducts is not more than one sixth of the total cutaneous ex- 

 udation ; but this, I believe, is altogether erroneous. When we recall 

 the impermeable nature of the horny and dried scales which constitute the 

 outer portion of the cuticle, and that these are constantly coated over with 

 an oily varnish issuing from the sebaceous glands, we may infer that the 

 cutaneous surface between the mouths of the perspiratory ducts is con- 

 structed rather for the hinderance of evaporation than for its promotion ; 

 and though the oily matter with which the skin is thus imbued is justly 

 regarded as having for one of its functions the prevention of injury from 

 the admission of external moisture, it must be equally effectual in stop- 

 ping the escape of water from within. The tardy manner in which wa- 

 ter thus escapes is illustrated by the operation of blisters. 



Under the form of steam, water continually escapes from the skin. It 

 also, on certain occasions, issues in the liquid state as drops 

 and perspira- of sweat. To its escape under the form of steam the desig- 

 nation of exhalation or insensible perspiration is given ; but if 

 under the form of sweat, that of sensible perspiration. 



OF EXHALATION. On condensing the vapors which arise from the 

 skin, they are found to consist of water containing a little acetate of am- 

 monia. With the water likewise escapes carbonic acid gas. With a 

 view of ascertaining the weight of the matters thus lost, Seguin inclosed 

 Experiments m 'mself in an air-tight bag, the mouth of which was gummed 

 to ascertain the upon his face in such a way as to permit the access of air to 

 tCTescapin g" tn respiratory organs. He then determined the weight of 

 through the his body and the bag together. After several hours, on re- 

 weighing, he ascertained the amount of loss by pulmonary 



