CUTANEOUS RESPIRATION. CUTANEOUS SECRETION. 535 



during rest has an acid reaction, while if the secretion is increased, the 

 acidity diminishes and the reaction may even become alkaline. The 

 sweat is composed of a glandular secretion having an alkaline reaction 

 and an acid epidermal secretion. The reaction will vary in accordance 

 with the preponderance of the one or the other of these constituents. 

 The constituents of the sweat : Water, together with volatile sub- 

 stances, and it increases after copious drinking, 991 parts in 1000. 

 E. Harnack found the solids on the average 8.5 in the thousand, includ- 

 ing organic matters, 2 in the thousand, and inorganic matters, 6.5 in the 

 thousand. Among the organic substances there should be mentioned 

 some neutral fats, palmitin, stearin, found also in the sweat of the palm of 

 the hand, which contains no sebaceous glands; in addition, cholesterin, 

 volatile fatty acids, principally formic acid, together with acetic, bu- 

 tyric, proprionic, caproic, and capric acids, probably varying qualitatively 

 and quantitatively in different portions of the body. They are present 

 in largest amount in the acid sweat first secreted. Further, there are 

 traces of sulphocyanid-combinations, of albumin (resembling casein), 

 considerable urea, more than o.i per cent., and also ammonium-salts 

 as decomposition -products of the latter in the air. Also sulphuric acid, 

 in conjugation with skatol and phenol, and oxyacids were found by 

 Kast in the sweat, uric acid by Tichborne. In the uremic state anuria 

 attending cholera urea is even found upon the skin in crystalline 

 form. 



Marked increase in the secretion of sweat in healthy persons and in uremic 

 patients diminishes the amount of urea in the urine. The reddish-yellow pigment 

 that alcohol extracts from the residue of sweat and that is colored green by oxalic 

 acid, is of unknown composition. 



Among the inorganic substances, those that are readily soluble pre- 

 ponderate over those that are soluble with difficulty. There have been 

 found sodium chlorid, 0.2; potassium chlorid, 0.02; sulphates, o.oi in 

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

 Of gases, the sweat contains carbon dioxid absorbed together with some 

 nitrogen. 



Of ingested substances, the following appear again in the sweat: readily, 

 benzoic acid, according to H. Meissner, also hippuric acid; cinnamic, tartaric, 

 succinic acids; with greater difficulty, quinin, potassium iodid, mercuric chlo- 

 rid, arsenous and arsenical acids, potassium and sodium arsenate. After the 

 ingestion of iron arsenite, iron is found in the urine and arsenous acid in the 

 sweat. Mercuric iodid is found transformed into chlorid, the iodin passing over 

 into the saliva. When ingested, sweat has toxic effects. 



Pigment- formation takes place in the form of a granular deposition, 

 principally in the deeper, and less in the upper layers of the Malpighian 

 network. It thus occurs particularly in the anal fold, on the scrotum, 

 and the nipple; as well as universally in the colored races. The horny 

 layer of the epidermis contains a diffuse yellowish-white pigment, which 

 becomes darker in old age. This pigment -format ion is supposed, like 

 the process of cornification, to depend upon a chemical process, in con- 

 sequence of which reduction takes place. This process is increased by 

 light. In addition, the prickle-layer contains granular pigment. The 

 dark discoloration of the epidermis can be removed and the process 

 of cornification can be prevented by means of free oxygen. 



Among pathological pigment-formations is that which occurs in liver-spots, 

 freckles, and in conjunction with Addison's disease. 



