394 EXCRETION. 



teen ounces). The estimates of Krause and of Valentin are a little less, but the difference 

 is not considerable. 



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

 and lungs may become very considerable. It is stated by Mr. Maclaren, the author of 

 an excellent work on training, that, in one hour's energetic fencing, the loss by perspira- 

 tion and respiration, taking the average of six consecutive days, was about three pounds, 

 or, accurately, forty ounces, with a range of variation of eight ounces. 



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

 the surface is immensely increased ; and it is by this rapid evaporation that persons have 

 been able to endure for several minutes a dry heat considerably exceeding that of 

 boiling water. Dr. South wood Smith made some very interesting 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 amounted to from two 

 to four pounds, this being chiefly by exhalation of watery vapor from the skin. In such 

 instances, the loss of water by transpiration is supplied constantly by the ingestion of 

 large quantities of liquid. 



Properties and, Composition of the Sweat. A very complete and satisfactory analysis 

 of the sweat was made by Favre, in 1853. After taking every precaution to obtain the 

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

 (fourteen litres), the result of six transpirations from one person, which he assumed to 

 represent about the average in composition. The liquid was perfectly 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 becomes alkaline on being subjected to evaporation, 

 showing that it contains some of the volatile acids. In the experiments of Favre, it was 

 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, con- 

 stantly alkaline. The specific gravity of the sweat is from 1003 to 1004. The following 

 is the composition of the fluid collected by Favre : 



Composition of the Sweat. 



Water 995-573 



Urea 0-043 



Fatty matters 1 0'014 



Alkaline lactates 0-317 



Alkaline sudorates 1'562 



Chloride of sodium, ") 2*230 



Chloride of potassium, 0*244 



Alkaline sulphates, j* soluble in water 0'012 



Alkaline phosphates, j a trace. 



Alkaline albuminates, J 0'005 



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



Epidermic debris (insoluble) a trace. 



1,000-000 



We have already alluded to the functions of the skin as a respiratory organ and its 

 office in regulating the temperature of the body by the evaporation of what is known as 

 the insensible perspiration ; but the composition of the sweat indicates clearly that the skin 

 is an important organ of excretion. Urea is now known to be a constant constituent of 

 the sweat, and the compounds of sudoric acid are probably excrementitious in their char- 

 acter, although they have not yet been detected in the blood or in any of the tissues. 

 The quantity of urea, under ordinary conditions, is not large ; but it is well known that its 

 proportion in the sweat is very much increased when there is deficient elimination by the 



