THE ANIMAL AS A MOTOR. 



69 



one to at least three. This quantity of work done 

 has no ascertained relation to the value of the energy 

 of the foods consumed ; although the work which an 

 animal can do is dependent upon the quantity of energy- 

 producing food which it can digest and assimilate under 

 the conditions to which it is subjected while at work. 

 The stored energy of the foods varies, according to 

 Frankland, from about 500 kilogrammes per gramme, or 

 45 foot-pounds per ounce, for lean meats, to three times 

 this quantity for the grain-foods and to six times this 

 value for butter; but the total need of the system 

 determines the kind and quality of food desirable at 

 any given time and for any given case. In general 

 the use of the grain-foods is, from a scientific and 

 possibly from a physiological point of view, most 

 productive of useful power in both man and the 

 domestic animals. Where the work is severe and long- 

 continued no time is allowed for proper digestion and 

 assimilation, and in such cases special care must be taken 

 to provide the best conditions for insuring endurance. 

 It is in illustration of this point that the case of the Arab 

 living on the coffee-berry, and the pedestrian on long 

 walks living entirely on the same material in the form 

 of a beverage, may be referred to. The warm drink is 

 at once stimulus and food, and demands Httle energy 

 in digestion and assimilation. A permanent dietary, 

 however, must contain all the elements demanded for 

 nutrition of all parts of the system in proper propor- 

 tions, and must at the same time provide the needed 

 mechanical and other stimuH of all the organs of the 

 body. The whole wheat used by man, fruits, and the 



* Nipher on Strength of the Muscle, Am. Jour. Sci., Nov. 1875. 



