i EXCHANGE OF MATEKIAL 3 



weight of his own body, and the influence of various external 

 conditions on those variations. 



He compared the weight of the food and drink taken daily 

 with that of the faeces and urine discharged. From these two 

 determinations and the variations in the weight of his body he 

 deduced the quantity of materials lost by insensible transpiration 

 through the skin and the lungs. 



It had long been known that the weight of an adult may 

 remain almost the same for months and years as the result of an 

 almost perfect balance between the intake and output of material. 

 It was also known that independently of the emptying of the 

 bladder and the bowels the body undergoes a slow and continuous 

 diminution in weight by transpiration. Sanctorius was, however, 

 the first who by long and patient labour measured the variable 

 quantity of this transpiration, and sought to demonstrate the 

 causes determining it. The balance between the intake and 

 output of material may be established not only for the sum total, 

 but also for the separate elements and chemical compounds 

 concerned. These studies only became possible after the discovery 

 of the respiratory gaseous exchange, and after chemistry was 

 sufficiently advanced to allow of the quantitative analysis of 

 the elements and compounds contained in the food taken and 

 in the urine and faeces discharged. 



The first important researches into total metabolism were 

 carried out by Boussingault, Sacc, Valentin, Barral, Dalton, and 

 Liebig between 1840 and 1850. Of the utmost importance is 

 the study of the metabolism of nitrogenous substances and the 

 balance of nitrogen, begun in a masterly way by Liebig, and 

 continued by Bischoff and Voit. Great also is the importance 

 of the gaseous exchange, and the balance of carbon, promoted by 

 the classic researches of Kegnault and Eeiset. 



Three different conditions of general metabolism may occur : 



() There may be almost perfect equality between the intake 

 and output of material, so that the balance of the animal economy 

 as a whole remains the same for a certain period, or is subject 

 to negative or positive variations of a slight and negligible 

 order. In. normal adults of middle age this state of equilibrium 

 may last for weeks, months, and even for years ; the weight of 

 the body ascertained daily at a fixed hour after the evacuations 

 and before a meal remains almost unchanged. 



(6) There may be an increase in the balance of the intake and 

 output of material, that is, there may be a gradual and variable 

 increase from day to day in the weight of the body. This occurs 

 during the whole of the normal anaplastic period or period of 

 growth, muscular development or the deposition of fat in the adult, 

 change from a meagre to a lavish or excessive diet in normal 

 individuals, and during convalescence after febrile disease. 



