282 ELEMENTARY PHYSIOLOGY less. 



The oxidation of the tissues, which are themselves built 

 up out of food, and lience ultimately the oxidation of the 

 food itself, thus provides for the energy expended as 

 muscular work and as heat. Now the amount of me- 

 chanical work a man does may be detremined with no 

 great difficulty, whether we calculate it as work done in 

 walking or in turning some machine or in some other 

 effort which results in overcoming a resistance. This 

 work is measured in terms of the resistance overcome, or 

 weight lifted, multiplied by the height through which it 

 is raised. Thus we speak of the work done in lifting one 

 pound through the height of one foot as a foot-pound ; 

 or using the metric system and taking a kilogramme 

 (2'2 lbs.) and a metre (39'37 inches) as the units of 

 weight and di.stance, we call the unit of work a kilo- 

 gramme-metre, equal to 7 '24 foot pounds. Using the 

 latter unit we may say that a good day's work is about 

 150,000 kilogramme-metres. 



The unit of heat is the amount of heat required to 

 raise the temperature of one pound of water through 

 1° F. Now, as is seen in all ortlinary engines, heat can 

 do work ; and it is found that one unit of heat can do 

 772 foot-pounds of work. This is called the " meclianical 

 equivalent of heat." In the metric system tlie unit 

 becomes the amount of heat required to raise the tem- 

 perature of one gramme (I5'4 grains) of water through 

 V C. This is called a calorie, and the mechanical 

 equivalent of heat is now 424 gramme metres. Using 

 tliese data we can readily convert heat into its equivalent 

 of Avork or vice versd. 



The measurement of the amount of heat given off by 

 the body is by no means easy, and the sources of error 

 are considerable. But allowing for these a rough deter- 

 mination may be made, and the heat thus measured may 

 be calculated as work by ucing the mechanical ecjuivalent 

 of heat and the result added to the actual work done as 

 work. The outcome of this calculation shows that of the 



