DISCUSSION OF RESULTS AND GENERAL CONCLUSIONS. 



91 



hour. This is due to a loss which has been known since the days of Sanctorius 1 

 as insensible perspiration. One of the best methods of observing this loss in 

 weight in the form of insensible perspiration is during the night. If, for 

 example, the subject is weighed just before going to bed and again in the morn- 

 ing immediately on rising and before the bladder is emptied, the loss in weight 

 will be due to insensible perspiration. Two such experiments were made with 

 a normal man weighing approximately 85 kilos, without clothing and a normal 

 woman weighing 65 kilos, without clothing. The results are shown in table 

 111, which gives the number of hours spent in bed and the loss in weight in 

 grams. The loss in weight was found to be directly proportional to the restless- 

 ness of the sleep, as on a hot, uncomfortable night it was much greater than on 

 a cold night when the person slept quietly beneath bedclothes, instinctively 

 moving no more than was necessary. On the average the man lost 39 grams 

 per hour and the woman 29 grams. The insensible perspiration, therefore, was 

 not far from 30 to 40 grams. 



Table 111. Loss in body-weight during night. 



Average loss per hour: Man, 39 grams; woman, 29 grams. 



This observation, made with a platform balance, of the loss of 30 to 40 

 grams of weight by insensible perspiration received substantiation from the 

 results of 50 or more experiments carried out in the Nutrition Laboratory by 

 more refined and exact methods. With a considerable number of individual 

 subjects it was found that the loss due to insensible perspiration, during wak- 

 ing hours, when the subject was sitting still 2 inside the respiration chamber, 

 averaged 40 grams per hour. In certain work experiments this insensible 

 perspiration was greatly increased, but it is safe to say that a normal person, 

 sitting still and reading quietly, will lose in weight approximately 40 grams 

 per hour. With severe muscular work the loss may be increased tenfold, or, 

 indeed, during the time of strenuous muscular exercise, as in athletic contests, 

 even a hundredfold. Although the amount of this insensible perspiration can 

 be obtained by accurately weighing the subject on scales, the character of the 

 loss can be determined only by careful respiration experiments, which show 

 that carbon dioxide and water-vapor are continually being given off from the 



'Sanctorius, De medicina statica aphorismi, Venice, 1614. Translated by John 

 Quincy, M. D., London, 1737. 



2 Benedict and Carpenter, Carnegie Institution of Washington Publication No. 126, 

 1910. p. 114. 



