512 VICTOR C. MYERS 



(he kidney. The excretion of magnesium and calcium are likewise inter- 

 related. 



Sweat 



Next to the kidneys, the skin is, in man, the most important channel 

 for the elimination of water. The volume eliminated varies widely under 

 different physiological and pathological conditions. Obviously the elimi- 

 nation in warm weather is much greater than in cold weather, also during 

 muscular activity than during rest. The specific gravity varies between 

 1.001 and 1.015, ordinarily amounting to about one-half the latter figure. 

 The solids range from about 0.4 to 2.0 per cent. The reaction may be acid, 

 neutral or alkaline to litmus, although under normal conditions it is most 

 often acid. Protein is generally present in traces. 



The skin excretes, qualitatively, practically the same substances as 

 occur in the urine, namely, urea, ammonia, uric acid, ainino-acids, crea- 

 tinin, chlorids, phosphates and sulphates. Probably for this reason it 

 lias been more or less generally accepted that the skin and kidneys can 

 act, to a certain extent, vicariously. At one time the use of sweat-baths 

 in the treatment of nephritis was common. The quantity of substances 

 excreted by the skin, however-, is quite insignificant in comparison to that 

 excreted by the kidney. In addition to their power to excrete water, the 

 sweat glands do appear to possess the power of excreting salt, the quantity 

 of sodium chlorid amounting to from 0.2 to 0.5 per cent. 



A variety of methods have been employed to collect sweat. Probably 

 the most satisfactory procedure is to place the patient in n rubber bag 

 during the sweating period. Sweat obtained in this way is a cloudy, 

 nearly colorless liquid, which settles or filters nearly or perfectly clear. 

 In the comparatively recent experiments of Riggs, and Plaggemeyer and 

 Marshal) this was the method employed. In his work on the cutaneous 

 excretion of nitrogen, where an attempt was made to determine the 

 twenty-four hour excretion, Benedict extracted the nitrogen from specially 

 prepared underwear. 



An idea of the composition of sweat obtained from normal subjects 

 and nephritic patients may be obtained from the table on the next page 

 compiled from the observations of Riggs. The sweat was obtained by 

 placing the subject without clothing in a rubber bag which enclosed the 

 entire body except the head. Sweating was induced by covering with a 

 pack of hot blankets for thirty to forty-five minutes. 



The observations on the nephritic patients are not especially signifi- 

 cant. It is of interest, however, that in the first two cases where the 

 volume of sweat is large the percentage of nitrogen is low and the chlo- 

 rids high, whereas in the last two cases where the volume is small, the 

 reverse is true. 



