446 INFLUENCE OF NERVES ON THE SECRETION OF SWEAT. 



of albumin (similar to casein) and urea, about 0*1 per cent. In ursemic conditions 

 (anuria in cholera) urea has been found crystallised on the skin. When the 

 secretion of sweat is greatly increased, the amount of urea in the urine is diminished, 

 both in health and in uneniia (Leiibe). The nature of the reddish-yellow pigment, 

 which is 'extracted from the residue of sweat by alcohol, and coloured green by 

 oxalic acid, is unknown. Amongst inorganic constituents, those that are easily 

 soluble are more abundant than those that are soluble with difficulty, in the pro- 

 portion of 17 to 1 ; sodium chloride, 0*2; potassium chloride, 0'2 ; sulphates, 0*01 

 per 1000, together with traces of earthy phosphates and sodium phosphate. Sweat 

 contains C0 in a state of absorption and some N. When decomposed with free 

 access of air, it yields ammonia salts (Gorup-Besanez). 



Excretion of Substances. Some substances when introduced into the body reappear in the 

 sweat benzoic, cinnaniic, tartaric, and succinic acids are readily excreted ; quinine and potassic 

 iodide with more difficulty. Mercuric chloride, arsenious and arsenic acids, sodium and 

 potassium arseniate have also been found. After taking arseniate of iron, arsenious acid has 

 been found in the sweat, and iron in the urine. Mercury iodide reappears as a chloride in the 

 sweat, while the iodine occurs in the saliva. 



Formation of Pigments. The leucocytes furnish the material, and the pigment 

 is deposited in granules in the deeper layers, and, to a less extent, in the upper 

 layers, of the rete Malpighii. This occurs in the folds around the anus, scrotum, 

 nipple, [especially during pregnancy], and everywhere in the coloured races. There 

 is a diffuse, whitish-yellow pigment in the stratum corneum, which becomes darker 

 in old age. The pigmentation depends on chemical processes, reduction taking 

 place, and these processes are aided by light. Granular pigment lies also in the 

 layers of prickle cells. The dark coloration of the skin may be arrested by free O 

 [hydric peroxide], while the corneous change is prevented at the same time 

 (Unna). 



Pathological. To this belongs the formation of liver spots or cholasma, freckles, and the 

 pigmentation of Addison's disease, [pigmentation round old ulcers, &c] ( 103, IV.). [The 

 curious cases of pigmentation, especially in neurotic women, e.g., in the eyelids, deserve further 

 study in relation to the part played by the nervous system in this process.] 



287. INFLUENCE OF NERVES ON THE SECRETION OF SWEAT. 



The secretion of the skin, which averages about -^ T of the body-weight, i.e., about 

 double the amount of water excreted by the lungs, may be increased or diminished. 

 The liability to perspire varies much in different individuals. The following con- 

 ditions influence the secretion 1. Increased temperature of the surroundings 

 causes the skin to become red, while there is a profuse secretion of sweat ( 214, 

 II., 1). Cold, as well as a temperature of the skin about 50 C, arrests the secretion. 

 2. A very watery condition of the blood, e.g., after copious draughts of warm 

 water, increases the secretion. Increased cardiac and vascular activity, whereby 

 the blood-pressure within the cutaneous capillaries is increased, have a similar effect ; 

 increased sweating follows increased muscular activity. 3. Certain drugs favour 

 sweating, e.g., pilocarpin, Calabar bean, strychnin, picrotoxin, muscarin, nicotin, 

 camphor, ammonia compounds; while others, as atropin and morphia, in large doses, 

 diminish or paralyse the secretion. [Drugs which excite copious perspiration, so 

 that it stands as beads of sweat on the skin, are called sudorifics, while those that 

 excite the secretion gently are diaphoretics, the difference being one of degree. 

 Those drugs which lessen the secretion are called antihydrotics.] 4. It is import- 

 ant to notice the antagonism which exists, probably upon mechanical grounds, 

 between the secretion of sweat, the urinary secretion, and the evacuation of the 

 intestine. Thus copious secretion of urine {e.g., in diabetes) and watery stools 

 coincide with dryness of the skin. If the secretion of sweat be increased, the 

 percentage of salts, urea, and albumin is also increased, whilst the other organic 

 substances are diminished. The more saturated the air is with watery vapour, the 

 sooner does the secretion appear in drops upon the skin, while in dry air or air in 



