376 EXTERNAL INTEGUMENT. 



the influence of the nervous system, which not only acts on 

 the vessels of the skin, but also directly on the glandular 

 elements ; hypersemia of the skin (as occasioned by extreme 

 heat), or great tension of the blood (such as is caused by the 

 absorption of a large quantity of water), no doubt serve to 

 increase the quantity of sweat, but the nervous system pro- 

 duces reflex secretions which are quite as energetic, and have 

 no resemblance to the congestion of the blood-vessels in the 

 skin ; if the blood does not furnish sufficient water for secre- 

 tion, a gland borrows its fluids from the neighboring tissues, 

 exactly as we have seen done by the salivary glands. The 

 profuse perspiration of death takes place when the skin is cold 

 and pale ; the common saying that certain emotions produce 

 cold sweats is perfectly correct. Indeed, the "nervous" con- 

 dition has the chief influence on sudation ; we perspire often 

 when some idea, such as fear, presents itself to our minds. 

 These sweats are often confined to some particular part of 

 the body, varying in different persons ; some very decided 

 reflex actions produce abundant perspiration round the waist, 

 or in some part of the face ; in cases of hemiplegia the sweat 

 appears only on one side of the body; if some drops of vine- 

 gar be placed upon the tongue and the mucous tissue of the 

 mouth, large drops of perspiration will appear on the fore- 

 head, or sometimes on one side of the forehead, or of the face. 

 The nervous organs for these reflex actions are not yet per- 

 fectly known ; their centre appears to be found in the spinal 

 cord. 



The sweat thus secreted by the sudoriferous coil, follows 

 the excretory tube, until it reaches the epidermis, the differ- 

 ent layers of which it traverses by means of a tube without 

 any proper walls, which is a hollow in the midst of these 

 layers. As the malpighian layer contains a large quantity of 

 fluid, and the corneous layer, properly so-called, is very 

 coherent, these layers derive nothing from the perspiration ; 

 but the most superficial layer, the pulverulent furfuraceous 

 or porous corneous layer, collects a large quantity in its inter- 

 stices. The perspiration, as it reaches this point, resembles 

 a river lost jn the sands; nearly all the fluid disappears. 

 Thus if the skin of a man in good health be touched, it is 

 found to be slightly damp, and produces an indefinable sensa- 

 tion, which is lacking during that period of a fever in which 

 the perspiration is entirely suppressed. It is only in cases 

 where the perspiration is extremely plentiful that it over- 

 flows, after being diffused through the pulverulent layer, and 



