ix THE SKIN AND CUTANEOUS GLANDS 489 



by the skin and lungs. On perspiring freely, as in summer, 

 micturition is scanty; in winter, on the contrary, when visible 

 perspiration is suspended, micturition is frequent and copious. 

 But apart from the influence of season and temperature in general, 

 clinical observation shows that in all cases in which there is 

 excessive loss by the kidneys and intestines (diabetes, diarrhoea) 

 this is compensated by a marked dry ness of the skin ; with the 

 opposite conditions the contrary is observed (nephritis, anuria). 



A good many fallacies prevail as to the intensity of cutaneous 

 perspiration. It is often stated, e.g., that not only the temperature, 

 but also the humidity of the surrounding atmosphere, increase 

 cutaneous secretion, whereas in reality the latter reduces evapora- 

 tion, or insensible perspiration, by increasing sweat, or sensible 

 perspiration. Frequent renewal of the air in contact with the 

 skin acts in the opposite sense : natural or artificial ventilation of 

 the atmosphere, within certain limits, does not perceptibly diminish 

 the cutaneous secretion, but it reduces sensible perspiration by 

 increasing evaporation. 



There is no constant relation between height of external 

 temperature and intensity of cutaneous secretion, the capacity 

 for sweating being very different for different individuals of the 

 same species. Caeteris paribus, however, perspiration in one and 

 the same individual increases in proportion with the external 

 temperature. In order to rouse the skin to a more active secretion 

 of sweat the external temperature must approximate to 33 C. 

 (Schierbeck, 1893). 



Besides external conditions, cutaneous secretion may be con- 

 siderably affected by alterations in the internal conditions, among 

 which are : (a) amount and quality of the food ingested, and 

 particularly what is drunk; (&) muscular activity or rest, which 

 respectively increase or diminish cardio-vascular activity ; (c) use 

 of certain drugs known as diaphoretics, e.g. pilocarpine, muscarine, 

 partially also nicotine and physostigmine (or the drugs which 

 have an opposite, antidiaphoretic action, e.g. atropine and daturine) ; 

 (d) sudden or violent mental emotions (anguish, anger, joy) which 

 increase the cutaneous secretion, independently of dilatation of 

 the cutaneous vessels (blushing), or their contraction (pallor). 



III. Since the external or internal conditions that promote or 

 hinder sweat secretion are so variable, it is easy to see why the 

 data collected by 'different observers as to the amount of sweat 

 secreted in the time-unit are of little general value. 



When collected in large quantities for purposes of analysis, the 

 sweat is a slightly turbid, almost colourless fluid, salt in taste, with 

 a more or less powerful rancid smell, due to the volatile fatty acids. 



In some regions, e.g. the axilla, groins, and pubis, the sweat 

 has a more penetrating odour, which may be highly unpleasant, 

 and is due to the special fatty acids mingled with the secretion. 



