824 '^^^^ POPULAR SCIENCE MONTHLY. 



pies may he looked upon as supplying the source 0/ power. The one 

 may be spoken of as holding the position of the instrument of action, 

 while the other supplies the motive power. Nitrogenous alimentary 

 matter may, it is true, by oxidation, contribute to the generation of the 

 moving force, but, as has been explained, in fulfilling this office there 

 is evidence before us to show that it is split up into two distinct por- 

 tions, one containing the nitrogen which is eliminated as useless, and a 

 residuary non-nitrogenous portio7i which is retained and utilized m 

 force-production.^^ 



The italics are mine, for reasons presently to be explained. The fol- 

 lowing pages of Pavy's work contain repetitions and illustrations of 

 this attribution of the origin of force to the non-nitrogenous elements 

 of food. 



Then we have a statement of the experiments of Joule on the me- 

 chanical equivalent of heat, connected with experiments of Frankland 

 with the apparatus that is used for determining the calorific value of 

 coal, etc., viz., a little tubular furnace charged with a mixture of the 

 combustible to be tested, and chlorate of potash (better a mixture of 

 chlorate and nitrate). This being placed in a tube, open below, and 

 thrust under water, is fired, and gives out all its heat to the surround- 

 ing liquid, the rise of temperature of which measures the calorific value 

 of the substance. 



From this result is calculated the mechanical work obtainable from 

 a given quantity of different food-materials. That from a gramme is 

 given as follows : 



Beef-fat 2'7,'7'78 "j 



Starch (arrow-root) 11,983 i Units of work, or number of 



Lump-sugar 10,254 i pounds lifted one foot. 



Grape-sugar 10,038 j 



In Dr. Edward Smith's treatise on " Food," the foot-pound equiva- 

 lent of each kind of food is specifically stated in such a manner as to 

 lead the student to conclude that this represents its actual working 

 efficiency as food. Other modern writers represent it in like manner. 



Here, then, comes the bearing of these theories on my subject. A 

 practical dietary or menu is demanded, say, for navvies or for ath- 

 letes in full work ; another for sedentary people doing little work of 

 any kind. 



According to the new theory, the best possible food for the first 

 class is fat, butter being superior to lean beef in the proportion of 

 14,421 to 2,829 (Smith), beef-fat having nearly eight times the value 

 of lean beef. Ten grains of rice give 7,454 foot-pounds of working 

 power, while the same quantity of lean beef only 2,829 ; according to 

 which one pound of rice should supply as much support to hard work- 

 ers as two and one half pounds of beefsteak. None of the modern 

 theorists dare to be consistent when dealing with such direct practical 

 applications. 



