i EXCHANGE OF MATERIAL 27 



both in proportion to the unit of weight and to the unit of body- 

 surface. Magnus-Levy found that a person of normal constitution 

 weighing 83 kgrms. absorbed 297 c.c. of oxygen per minute, 

 and a stout person weighing 100 kgrms. 307 c.c. per minute, 

 that is, the former absorbed 3'6 c.c., the latter 2'8 c.c. per kgrm. 

 (almost 25 per .cent less). The former used 125 c.c., the latter 

 108 c.c. per square metre of surface. This difference proves that 

 not the body-surface, but the constitution exercises the greatest 

 influence on the intensity of combustion. It is a fact well known 

 to every one that a too sedentary life is favourable to the accumu- 

 lation of fat in the organism, whilst an active' life and regular 

 exercise develop the muscles and favour the consumption of fat. 

 After such a constitutional change, there is an increase of about 

 10 per cent in the combustion. In dogs which have been for 

 long trained to perform muscular work, a remarkable increase in 

 the consumption of oxygen during rest has been observed, as 

 compared with that found before such training. 



VII. If an animal be kept fasting for several days and then 

 fed, the metabolism which had gone down during the period of 

 abstinence immediately increases, even if the quantity of food 

 taken be very small. I proved this to be the case with Succi on 

 the twenty-fifth and twenty-sixth days of his fast, by giving him 

 small quantities of gelatine and peptone respectively. 



It is not possible to preserve the organism in the state of 

 nutrition obtaining after a fast lasting several days, by giving it 

 a supply of food, both nitrogenous and non-nitrogenous, corre- 

 sponding to the daily loss of nitrogen and carbon. Each time 

 food is given the metabolism of the tissues is stimulated to 

 greater activity, so that the organism consumes more than when 

 fasting, the output is therefore greater than the intake, and the 

 weight of the body decreases, though more slowly than during 

 absolute fasting. If we increase the nourishment gradually, the 

 difference between the intake and output will diminish, at first 

 more rapidly, afterwards more slowly, and finally attain an almost 

 perfect equilibrium. This equilibrium is reached when about 

 twice or three times as much nitrogen and about one-and-a-half 

 times as much carbon are given in the food as the animal lost 

 daily during its fast. 



If a dog be kept for several days on a meagre diet of 

 nitrogenous food, such as lean horse-flesh, so that there is a 

 deficit in the daily balance of nitrogen, and is then given enough 

 nitrogen to make up for the losses sustained, there is for 

 some days a gain in the balance of nitrogen, that is, the intake 

 of nitrogen will exceed the output. This gain will, however, 

 gradually diminish, until in a few days nitrogenous equilibrium 

 is attained ; i.e. the meat consumed is equal to that received. 



If the animal in a state of equilibrium on a plentiful meat 



