490 PHYSIOLOGY CHAP. 



When examined under the microscope, the sweat shows a 

 number of epidermoid scales detached from the surface of the 

 skin, as well as fat-granules. 



Human sweat gives an acid reaction under ordinary conditions ; 

 in the horse and cat it is almost always alkaline (Luchsinger). 

 The acidity of human sweat is due to the fatty acids. Some 

 authors hold that this depends on the admixture of the secretion 

 from the sebaceous glands, and state that in parts where the 

 latter are absent, e.g. the palm of the hand after well washing, 

 the sweat has an alkaline reaction (Tourton) ; others again 

 contradict this observation (Franc,ois-Franck, Albini). Since we 

 know (supra) that many coiled glands have throughout life a 

 function that differs in no way from that of the sebaceous glands, 

 it seems logical to assume that the coiled glands which do serve 

 the sudorific function also secrete along with the sweat a small 

 amount of sebum, which (infra) is rich in fatty substances of 

 various kinds, and gives to the whole secretion its acid reaction. 

 Trlimpy and Luchsinger (1878) established the important fact 

 that during profuse sweating the acidity of human sweat gradually 

 diminishes till it becomes neutral, and is eventually alkaline like 

 that of the horse. This phenomenon is easily explained on the 

 assumption that the acid sebum of the secretion, which is a slowly 

 formed product of the secretory cells, is easily exhausted, while 

 the watery sweat, which has the alkaline reaction of the blood 

 and lymph from which it is derived, persists. 



Various methods have been tried for collecting the products of cutaneous 

 secretion from the whole surface of the body or from any part of it. If the 

 forearm is enclosed in a rubber bag, with a glass bottle at one end, evapora- 

 tion from the skin is checked, and the whole of the exudate runs into the 

 bottle in the form of sweat (Anselniino, 1844). The subject may be enclosed 

 in a Pettenkofer and Yoit's respiration chamber, breathing through a rubber 

 mask applied to the month and nostrils, with tubes attached. Comparison 

 of the water and carbon dioxide of the air that enters and leaves the 

 chamber gives the sum of the products evaporated from the entire 

 cutaneous surface (Schierbeck, 1893). If the subject is enclosed in a 

 receptacle (with the exception of the head), and the temperature of the 

 surrounding air is raised, a copious secretion of sweat is induced from the 

 whole cutaneous surface, and collects at the bottom of the receiver (Favre, 

 1852). By the simpler method of the so-called vapour -bath, which is 

 produced by raising the temperature of the surrounding atmosphere, it is 

 possible to collect the greater part of the sweat that runs off the skin, so as to 

 determine its content of organic substances (Argutinsky, 1890). 



Quantitative analyses of the principal organic and mineral 

 constituents of the sweat led to widely dissimilar results, according 

 to Schottin (1851), Favre (1852), Funke (1858). All the analyses, 

 however, point to the fact that sweat is the most watery of all 

 the secretions, since it contains not more than 0'5-1'5 per cent 

 solids, of which about | consists of mineral substances, mainly 

 sodium chloride. The following table, drawn up by Harnack, gives 



