444 CUTANEOUS RESPIRATION: SEBUM SWEAT. 



cutaneous fatty tissue than through the skin alone ; the epidermis conducts heat 

 less easily than the fat and the chorium. 



The solid, elastic, easily movable cutis affords a good protection against external, 

 mechanical injuries; while the dry, impermeable, horny epidermis, devoid of 

 nerves and blood-vessels, affords a further protection against the absorption of 

 poisons, and at the same time it is capable of resisting, to a certain degree, thermal 

 and even chemical actions. A thin layer of fatty matter protects the free surface of 

 the epidermis from the macerating action of fluids, and from the disintegrating 

 action of the air. The epidermis is important in connection with the fluids of the 

 body. It exerts pressure upon the cutaneous capillaries, and, to a limited extent, 

 prevents too great diffusion of fluid from the cutaneous vessels. Parts of the skin 

 devoid of epidermis are red and always moist. When dry, the epidermis and the 

 epidermal appendages are bad conductors of electricity ( 326). Lastly, the exist- 

 ence of uninjured epidermis prevents adjoining parts from growing together. 



As the epidermis is but slightly extensile it is stretched over the folds and papillae of the cutis 

 vera, which becomes level when the skiu is stretched, and the papillae may even disappear with 

 strong tension {Leunnski). 



286. CUTANEOUS RESPIRATION: SEBUM SWEAT. The skin, with a 

 surface of more than 1 J square metre, has the following secretory functions : 



1. The respiratory excretion ; 



2. The secretion of sebaceous matter ; and 



3. The secretion of sweat. 



[Besides this the skin is protective, contains sense-organs, is largely concerned 

 in regulating the temperature, and may be concerned in absorption.] 



1. Eespiration by the skin has been referred to ( 131). The organs concerned are the tubes 

 of the sweat-glands, moistened as they are with fluids, and surrounded by a rich network of 

 capillaries. It is uncertain whether or not the skin gives off a small amount of N" or ammonia. 

 Ri>hrig made experiments upon an arm placed in an air-tight metal box. According to him 

 the amount of C0. 2 and H0 excreted is subject to certain daily variations ; it is increased by 

 digestion, increased temperature of the surroundings, the application of cutaneous stimuli, and 

 by impeding the pulmonary respiration. The exchange of gases also depends upon the vascu- 

 larity of certain parts of the skin, while the cutaneous absorption of also depends upon the 

 number of coloured corpuscles in the blood. 



In frogs and other amphibians, with a thin, always moist epidermis, the cutaneous respir- 

 ation is more considerable than in warm-blooded animals. In winter, in frogs, the skin alone 

 yields of the total amount of CO., excreted ; in summer, of the same {Bidder) ; thus, in 

 these animals it is a more important respiratory organ than the lungs themselves. 



Suppression of the cutaneous activity by varnishing or dipping the skin in oil, causes death 

 by asphyxia (frogs) sooner than ligature of the lungs. Varnisning the Skin. When the skin 

 of a warm-blooded animal is covered with an impermeable varnish [such as gelatin] {Fourcaidt> 

 Becqucrcl, Brecliet), death occurs after a time, probably owing to the loss of too much heat. 

 The formation of crystalline ammonio-magnesic phosphate in the cutaneous tissue of such 

 animals {Edenhuizen) is not sufficient to account for death, nor are congestion of internal 

 organs and serous effusions satisfactory explanations. The retention of the volatile substances 

 (acids) present in the sweat is not sufficient. Strong animals live longer than feeble ones ; 

 horses die after several days {Gerlach) ; they shiver and lose flesh. The larger the cutaneous 

 surface left unvarnished, the later does death take place. Rabbits die when of their surface 

 is varnished. When the entire surface of the animal is varnished, the temperature rapidly 

 falls (to 19), the pulse and respirations vary ; usually they fall when the varnishing process is 

 limited ; increased frequency of respiration has been observed ( 225). Pigs, dogs, horses, when 

 one-half of the body is varnished, exhibit only a temporary fall of the temperature, and show 

 signs of weakness, but do not die {Ellenberger and Hofmcister). [In extensive burns of the 

 skin, not only is there disintegration of the coloured blood-corpuscles (v. Lesser), but in some 

 cases ulcers occur in the duodenum. The cause of the ulceration, however, has not been ascer- 

 tained satisfactorily {Curling).] 



2. Sebaceous Secretion. The fatty matter as it is excreted from the acini of 

 the sebaceous glands is fluid, but even within the excretory duct of the gland it 

 stagnates and forms a white fat-like mass, which may sometimes be expressed (at 

 the side of the nose) as a worm-like white body, the so-called comedo. The 



