138 EXCKETION. 



to the mechanism of its separation 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 this secretion 

 is remarkable. It is well known, for example, that an abun- 

 dant production of perspiration is frequently the result of 

 mental emotions. Bernard has shown, in a series of inter- 

 esting experiments, that the nervous influence may be prop- 

 agated through the sympathetic system. In one of these 

 observations, he divided the sympathetic in the neck of a 

 horse, producing, as a consequence, an elevation in tempera- 

 ture and 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. 1 "When the skin is in a normal con- 

 dition, after exercise or whenever there is a tendency to ele- 

 vation 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 ex- 

 posed to a high temperature ; and it is by an increase in the 

 transpiration from the surface that the animal heat is main- 

 tained at the normal standard. 



Quantity of Cutaneous Exhalation. The amount of 

 cutaneous exhalation is subject to great variations, depend- 



of perspiratory tubing is nearly twenty-eight miles. In a note, however, it is 

 stated that the sebiparous system is included in this calculation (ERASMUS WIL- 

 SON, Healthy Skin, Philadelphia, 1854, p. 63). 



1 BERNARD, Liguides de Forganisme, Paris, 1859, tome ii., p. 183. 



