THE CHEMISTRY OF COOKERY. 821 



from my immediate subject. (Dr. Pavy's " Treatise on Food " has 

 an introductory chapter on " The Dynamic Relations of Food," in 

 which this subject is clearly treated in sufficient detail for popular 

 reading.) 



It is quite the fashion now to rely upon these later experiments ; 

 but, for my own part, I am by no means satisfied with them — and for 

 this reason, that the perspiration from the skin and the vapor from the 

 lungs were not examined. It is just these which are greatly increased 

 by exercise, and their quantity is very large, especially those from the 

 skin, which are threefold, viz., the insensible perspiration, which is 

 transpired by the skin as invisible vapor ; the sweat, which is liquid ; 

 and the solid particles of exuded cuticle. 



Lavoisier and Seguin long ago made very laborious experiments 

 upon themselves in order to determine the amount of the insensible 

 perspiration. Seguin inclosed himself in a bag of glazed taffeta, which 

 was tied over him with no other opening than a hole corresponding to 

 his mouth ; the edges of this hole were glued to his lips with a mixt- 

 ure of turpentine and pitch. He carefully weighed himself and the 

 bag before and after his inclosure therein. His own loss of weight 

 being partly from the lungs and partly from the skin, the amount 

 gained by the bag represented the quantity of the latter ; the differ- 

 ence between this and the loss of his own weight gave the amount 

 exhaled from the lungs. 



He thus found that the largest quantity of insensible exhalation 

 from the lungs and skin together amounted to three and a half ounces 

 per hour, or five and a quarter pounds per day. The smallest quantity 

 was one pound fourteen ounces, and the mean was three pounds eleven 

 ounces. Three fourths of this was cutaneous. 



These figures only show the quantity of insensible perspiration dur- 

 ing repose. Valentin found that his hourly loss by cutaneous exhala- 

 tion while sitting amounted to 32*8 grammes, or rather less than one 

 and a quarter ounce. On taking exercise, with an empty stomach, in 

 the sun, the hourly loss increased to 89'3 grammes, or nearly three 

 times as much. After a meal followed by violent exercise, with the 

 temperature of the air at 72° Fahr., it amounted to 132*7 grammes, or 

 nearly four and a half times as much as during repose. A robust man, 

 taking violent exercise in hot weather, may give off as much as five 

 pounds in an hour. 



The third excretion from the skin, the epithelial or superficial 

 scales of the epidermis, is small in weight, but it is solid, and of similar 

 composition to gelatine. It should be understood that this increases 

 largely with exercise. The practice of sponging and " rubbing down " 

 of athletes removes the excess ; but I am not aware of any attempt 

 that has been made to determine the quantity thus removed. 



Does the skin excrete nitrogenous matter that may be, like urea, 

 a product of the degradation or destruction of muscular tissue ? 



