PROPERTIES AND COMPOSITION OF THE SWEAT. 357 



and exhaled in the twenty-four hours. Seguin and Lavoisier (1790) esti- 

 mated the daily quantity of cutaneous transpiration at one pound and four- 

 teen ounces (850 grammes), and the results of their observations have been 

 fully confirmed by recent investigations. It may be assumed that the aver- 

 age quantity is nearly two pounds, or about 900 grammes. 



Under violent and prolonged exercise, the loss of weight by exhalation 

 from the skin and lungs may become very considerable. It is stated by 

 Maclaren, the author of a work on training, that in one hour's energetic 

 fencing, the loss by perspiration and respiration, taking the average of six 

 consecutive days, was forty ounces (1,130 grammes), with a range of variation 

 of eight ounces (227 grammes). 



When the body is exposed to a high temperature, the exhalation from the 

 surface is largely increased ; and it is by this rapid evaporation that persons 

 have been able to endure for several minutes a dry heat considerably exceed- 

 ing that of boiling water. Southwood Smith made a series of observations 

 with regard to this point upon workmen employed about the furnaces of gas- 

 works and exposed to intense heat ; and he found that in an hour, the loss of 

 weight was two to four pounds (907 to 1,814 grammes), this being chiefly by 

 exhalation of watery vapor from the skin. In such instances the loss of water 

 by transpiration is compensated by the ingestion of large quantities of liquid. 



Properties and Composition of the Sweat. An analysis of the sweat was 

 made by Favre, in 1853. After taking every precaution to obtain the secre- 

 tion in a perfectly pure state, he collected a very large quantity, nearly thirty 

 pints (14 litres), the result of six transpirations from one person, which he 

 assumed to represent about the average in composition. The liquid was per- 

 fectly limpid, colorless, and of a feeble but characteristic odor. Almost all 

 observers have found the reaction of the sweat to be acid ; but it readily be- 

 comes alkaline on being subjected to evaporation, showing that it contains 

 some of the volatile acids. Favre found that the fluid collected during the 

 first half-hour of the observation was acid ; during the second half-hour it 

 was neutral or feebly alkaline ; and during the third half-hour, it was con- 

 stantly alkaline. The specific gravity of the sweat is 1003 to 1004. The fol- 

 lowing is the composition of the fluid collected by Favre : 



COMPOSITION OF THE SWEAT. 



Water 995-573 



Urea 0-043 



Fatty matters 0-014 



Alkaline lactates 0-317 



Alkaline sudorates 1-562 



Sodium chloride, ~\ 2-230 



Potassium chloride, 0-244 



Alkaline sulphates, I soluble in water 0-012 



Alkaline phosphates, a trace 



Alkaline albuminates, J 0-005 



Alkaline earthy phosphates (soluble in acidulated water) '. . . a trace 



Epidermic debris (insoluble) a trace 



1,000-000 



