Insensible Perspiration. 113 



weight from minute to minute. During the day the frequent drinking of 

 water, taking of food, passing of urine, and defecation, tend to obscure the 

 fact that there is this persistent loss in weight. On the other hand, body- 

 weights taken immediately before retiring at night and immediately on rising 

 in the morning before urine is passed or water drunk show a loss in weight 

 which is reasonably constant with uniform conditions. 



Experiments ox Loss During the Night. 



A series of experiments made by one of us shows very conclusively that the 

 loss in body-weight during the night may be studied with considerable accuracy 

 by means of platform scales weighing to within 10 grams. These are so-called 

 " silk scales " and are inexpensive. The observations which were made on 

 2 persons, one a man and the other a woman, showed that the loss in body- 

 weight during the night was relatively constant. The fluctuations were due 

 in large part to changes in temperature of the season. On hot nights with a 

 high degree of humidity, when the subjects were more or less restless, the loss 

 in weight was very noticeable. On cold nights, when the subjects remained 

 quietly covered with bed-clothing, the loss in weight was at a minimum. This 

 is somewhat contrary to expectation, as we would naturally expect less vaporiza- 

 tion of Avater in moist air. Apparently the restlessness more than compensated 

 the possible decrease in vaporization. 



INSENSIBLE PERSPIRATION IN CONNECTION WITH METABOLISM EXPERIMENTS. 

 Method of Obtaining Insensible Loss by Calculation. 



In the experiments here reported, the body-weight was carefully recorded by 

 means of a platform scale similar to the type mentioned above. This scale 

 was arranged outside of the respiration calorimeter in accordance with the plan 

 shown in a previous publication. 1 



The subject was weighed sitting in an arm-chair suspended from the scale, 

 and under most advantageous conditions the body-weight could be recorded to 

 within 2 to 4 grams. Consequently, during experiments in which the body- 

 weight was carefully recorded at the beginning and end, and the urine, drink- 

 ing water, food, and feces were carefully weighed, it is possible to compute the 

 insensible perspiration from hour to hour. A simple illustration will serve to 

 show this. With one subject the body-weight at the beginning of an experi- 

 ment was 68,220 grams; at the end of the experiment, ? h 15 m later, the body- 

 weight was 68,904 grams. There was then, as recorded by the balance, an 

 increase in weight of 684 grams, but during this period the subject ate 1049 

 grams of food and drank 136 grams of water and there were 188 grams of 

 urine voided. Consequently, making allowances for the food, drink, and urine, 



1 Atwater and Benedict, Carnegie Institution of Washington Publication No. 42, 

 1905, p. 159. 



