CHAP, v.] NUTRITION. 803 



If we translate the units of heat into units of work, the 

 2,310,000 gramme-degree, or 2,310 kilogramme degree calorics 

 will give us about IKSO.OOO, or, in round numbers, somewhere 

 about one million kilogramme-meters. 



\Vc may, in passing, call attention to the fact that the 

 proteids supply a relatively small part of the total energy, and 

 that the share contributed by the large mass of carbohydrates is not 

 much greater than that belonging to the much smaller quantity 

 of fat. In the average diet obtained by the statistical method, in 

 which the data are largely drawn from public institutions, the 

 (cheaper) carbohydrates are still further increased at the expense 

 of the (dearer) fats, a change which may tend to reduce somewhat 

 the total energy ; but this does not materially affect the broad 

 result just given. 



The Expenditure. 



528. There are two ways only in which energy is set free 

 from the body : mechanical labour and heat. The body loses 

 energy in producing muscular work, as in locomotion and in 

 other kinds of labour, in the movements of the air in respiration 

 and speech, and, though to a hardly recognizable extent, in the 

 movements of the air or contiguous bodies by the pulsations of 

 the vascular system. The body loses energy in the form of heat 

 by conduction and radiation, by respiration and perspiration, and 

 by the warming of the urine and fasces. All the internal work of 

 the body, all the mechanical labour of the internal muscular 

 mechanisms with their accompanying friction, all the molecular 

 labour of the nervous and other tissues, is converted into heat 

 before it leaves the body. The most intense mental action, 

 unaccompanied by any muscular manifestations, the most energetic 

 action of the heart or of the bowels, with the slight exceptions 

 mentioned above, the busiest activity of the secreting or metabolic 

 tissues, all these end simply in augmenting the expenditure in 

 the form of heat. 



A normal daily expenditure in the way of mechanical labour 

 can be easily determined by observation. Whether the work take 

 on the form of walking, or of driving a machine, or of any kind 

 of muscular toil, a good day's work may be put down at about 

 150,000 kilogramme-meters. 



The normal daily expenditure in the way of heat cannot be so 

 readily determined. Direct calorimetric observations on the whole 

 body are attended with so many difficult irs. except in the case of 

 small animals, that their value is uncertain ; and observations 

 made by placing a part only of the body, an arm or leg for 

 example, in the calorimeter, and from the data thus gained 



512 



