386 CUTANEOUS RESPIRATION. [BOOK 11. 



temperature conduces, as we shall point out presently, to an in- 

 crease of the secretion, and it is possible that mere dryness of the 

 air has a similar effect. 



The total amount of perspiration is affected not only by the 

 condition of the atmosphere, but also by the nature and quantity 

 of food eaten, by the amount of fluid drunk, and by the amount of 

 exercise taken. It is also influenced by mental conditions, by 

 medicines and poisons, by diseases, and by the relative activity of 

 the other excreting organs, more particularly of the kidney. 



The fluid perspiration, or sweat, when collected, is found to be 

 a clear colourless fluid, with a strong and distinctive odour varying 

 according to the part of the body from which it is taken. Besides 

 accidental epidermic scales, it contains no structural elements. 

 The reaction of the secretion of the sweat glands, apart from that 

 of the sebaceous glands, appears to be alkaline. This is well seen 

 when the sweat becomes abundant. An admixture of sebaceous 

 secretion may, when the sweat itself is scanty, give rise to an acid 

 reaction, probably from the sebaceous fats becoming converted into 

 fatty acids. The average amount of solids is about 1'81 p.c., of 

 which about two-thirds consist of organic substances. The chief 

 normal constituents are: (1) Sodium chloride with small quantities 

 of other inorganic salts. (2) Various acids of the fatty series, 

 such as formic, acetic, butyric, with probably propionic, caproic, 

 and caprylic. The presence of these latter is inferred from the 

 odour ; it is probable that many various volatile acids are present 

 in small quantities. Lactic acid, which Berzelius reckoned as a 

 normal constituent, is stated not to be present in health. (3) 

 Neutral fats, and cholesterin; these have been detected even in 

 places, such as the palms of the hand, where sebaceous glands are 

 absent. (4) Though some observers seem to have found a consider- 

 able quantity of urea (calculated at 10 grms. in the 24 hours for 

 the whole body) in sweat, the evidence goes to shew that neither 

 urea nor any ammonia compound exists in the normal secretion to 

 any extent ; apparently some small amount of nitrogen leaves the 

 body by the skin, but this is probably supplied by the epidermis. 



In various forms of disease the sweat has been found to contain, 

 sometimes in considerable quantities, blood, albumin, urea (par- 

 ticularly in cholera), uric acid, calcium oxalate, sugar, lactic acid, 

 indigo, bile and other pigments. Iodine and potassium iodide, 

 succinic, tartaric, and benzoic (partly as hippuric) acids have been 

 found in the sweat when taken internally as medicines. 



Cutaneous Respiration. 



A frog, the lungs of which have been removed, will continue to 

 live for some time ; and during that period will continue not only 

 to produce carbonic acid, but also to consume oxygen. In other 



