PERSPIRATION. 393 



and abdomen, 1,136 ; on the back of the neck, the back, and the nates, 417; on the fore- 

 arm, inner surface, 1,123, and the outer surface, 1,093; on the hand, palmar surface, 

 2,736, and dorsal surface. 1,490 ; on the upper part of the thigh, inner surface, 576, outer 

 surface, 554; on the lower part of the thigh, inner surface, 576; on the foot, plantar 

 surface, 2,685, and dorsal surface, 924. From these figures, it is estimated that the 

 entire number of perspiratory glands is 2,381,248; and, assuming that each coil when 

 unravelled measures about -j- 1 ^ of an inch, the entire length of the secreting tubes is 

 about 2 miles. It must be remembered, however, that the length of the secreting coil 

 only is given, and that the excretory ducts are not included. 



Mechanism of the Secretion of Sweat. The action of the skin as a glandular organ is 

 continuous and not intermittent ; but, under ordinary conditions, the sweat is exhaled 

 from the general surface in the form of vapor. With regard to the mechanism of its sepa- 

 ration from the blood, nothing is to be said in addition to the general remarks upon the 

 subject of secretion ; and it is probable that the epithelium of the secreting coils is the 

 active agent in the selection of the peculiar matters which enter into its composition. 

 There are no examples of the separation by glandular organs of vapor from the blood, 

 and the perspiration is secreted as a liquid, and only becomes vaporous as it is discharged 

 upon the surface. 



The influence of the nervous system upon the secretion of sweat is remarkable. It is 

 well known, for example, that an abundant production of perspiration is frequently the 

 result of mental emotions. Bernard has shown, in a series of interesting experiments, that 

 the nervous influence may be propagated through the sympathetic system. In one of these 

 observations, he divided the sympathetic in the neck of a horse, producing, as a conse- 

 quence, an elevation in temperature and an increase in the arterial pressure in the part 

 supplied with branches of the nerve. He found, also, that the skin of the part became 

 covered with a copious perspiration. Upon galvanizing the divided extremity of the nerve, 

 the secretion of sweat was arrested. When the skin is in a normal condition, after exer- 

 cise or whenever there is a tendency to elevation of the animal temperature, there is a 

 determination of blood to the surface, accompanied with an increase in the secretion of 

 sweat. This is the case when the body is exposed to a high temperature ; and it is by 

 an increase in the transpiration from the surface that the animal heat is maintained at the 

 normal standard. 



Quantity of Cutaneous Exhalation. The amount of cutaneous exhalation is subject 

 to great variations, depending upon conditions of temperature and moisture, exercise, the 

 quantity and character of the ingesta, etc. Most of these variations relate to the func- 

 tion of the skin in regulating the temperature of the body ; and it is probable that the 

 elimination of excrementitious matters by the skin is not subject, under normal condi- 

 tions, to the same modifications, although positive experiments upon this point are want- 

 ing. It is not designed, in this connection, to discuss all the experiments that have been 

 made upon the quantity and the modifications of the cutaneous exhalations, and we shall 

 consider only what appear to be the most reliable of the numerous recorded observations 

 upon this subject. The classical experiments of Sanctorius were among the first at- 

 tempts to determine by the balance the relations of the ingesta to the exhalations ; but 

 these were necessarily imperfect, on account of the difficulty in constructing proper in- 

 struments for the investigations, and the cutaneous and pulmonary exhalations were esti- 

 mated together. When there is such a wide range of variation in different individuals 

 and in the same person under different conditions of season, climate, etc., it is only pos- 

 sible to give approximate estimates of the quantity of sweat secreted and exhaled in the 

 twenty-four hours ; and more recent observations have shown that the calculations of 

 Seguin and Lavoisier, made in 1790, are very nearly correct. These observers estimated 

 the daily quantity of cutaneous transpiration at about two pounds (one pound and four- 



