THE STORY OF THE LUNGS, SKIN AND KIDNEYS 99 



means large. Even the best constructed machine 

 will only give a very limited percentage of power 

 when compared with the amount of fuel it consumes. 

 The case is extremely different with the human 

 engine, for on a comparatively small amount of fuel 

 it gives an amount of energy which is positively 

 startling when we come to sum up the various items 

 whereof it is composed. If we calculated the power 

 developed by the body as a living engine out of the 

 food it consumes, we find that according to one calcu- 

 lation, the internal work, that of maintaining the body 

 itself, may be reckoned as equal to 2,800 foot tons 

 per day that is to say, if applied in the shape of 

 mechanical work, this amount of energy would be 

 capable of raising 2,800 tons one foot from the 

 ground. The same estimate maintains that an 

 ordinary day's work, about 300 foot tons, will 

 really be increased five times, namely, 1,500 foot tons, 

 in addition to the quantity required for the body's 

 own maintenance. Thus we get 1,500 foot tons plus 

 2,800, or 4,300 foot tons in all, developed from the 

 fuel supplied to us in the shape of our food. This 

 tremendous amount of working power represents the 

 profit we obtain from the transactions we carry out 

 every day, in the way of obtaining our food, and of 

 assimilating it and digesting it. If the amount of 

 power expended in the work we perform daily, apart 

 from the internal work of the body, be calculated, a 

 man at light work develops from 150 to 200 foot tons 

 per day. The average work is estimated at from 

 300 to 350 foot tons in the case of a hard worker. 

 In the case of a hard worker he may develop between 

 450 and 500 foot tons, and in laborious work between 

 500 and 600 foot tons. Another mode of calculation 

 teaches us that out of his daily food a man requires 



