The changes that occur in the body weight of normal persons from day to day or hour to hour are usually unnoticed, probably because they are relatively slight, and because attention has not been directed to such changes. It has long been recognized, however, that muscular exercise and severe work will cause a considerable loss in body weight, both through increased loss of water and through actual breakdown of the constituents of the body.
Benedict1 in Boston is perhaps the foremost advocate of the clinical application of computing the metabolism by measuring the loss of weight caused by the insensible perspiration. He gives an excellent summary of the literature on this subject from the time of Sanctorius in 1614 until the present. The insensible perspiration has been defined (Benedict) as "those gaseous emanations from the body which do not appear in the form of sensible moisture or sweat, in
WILSON GE. INSENSIBLE PERSPIRATION: ITS RELATION TO BASAL METABOLISM. Arch Intern Med (Chic). 1933;52(3):378-383. doi:10.1001/archinte.1933.00160030039003