THE ANIMAL AS A PRIME MOVER. 307 



called foods, such as potatoes, carrots and turnips, contain three-fourths 

 to seven-eighths their weight water, and only supply from 800 to 1.800 

 British thermal units of energy. In foot-pounds of dynamic power, the 

 figures are 600,000 to 1,400,000 for the last-mentioned substances, 

 1,500,000 or 2,300,000 for the lean meats, 5,000,000 to 6,000,000 for the 

 grain foods, and 12,000,000 for the fats per pound of nutriment digested. 

 This comparison, however, gives no clew to their value as foods and as 

 nutriment of the vital machine, since it is known that the heat-produc- 

 ing value is but a part of the question, and that the power of assimi- 

 lating the elements of the body and of producing muscle, nerve, brain 

 and bone is no less essential to the maintenance of the efficiency of the 

 machine than the production of thermal or other equivalent energies. 

 The grains have double the value of tbe meats as brain and nerve 

 foods, and the coarse vegetables one-fourth the value of the grains in 

 this respect. Butter and lard, the best heat producers, have no value 

 at all as muscle and nerve material. 1 



Voit and others give the correct proportion of these elements in good 

 food as about 120 grams protein, 50 grams of fats, 550 grams of carbo- 

 hydrates, a total of say, 700 grams, about 23 ounces per day, as the 

 requirement of a man doing a day's work at muscular labor. This 

 provides not far from 3,000 calories of thermal energy by oxidation. 

 Voit gives a total required energy in thermal units of from 3,000 to 

 3,300 calories, Playfair from 3,000 to 3,700, and Atwater from 2,820 

 to 4,0G0 calories ; or, collecting all the best authorities, we may say that 

 3,000 calories, about 12,000 British thermal units, may be taken as 

 representative of the demand of the machine for energy when doing 

 little external work, and 4,000 calories, about 16,000 British thermal 

 units, when performing a hard day's work every day. This means the 

 equivalent of 1 pound of ordinary coal for the first, and an equal 

 weight of the best coal for the second case, burned completely and with, 

 consequently, maximum production of thermal energy and dynamic 

 power. One pound of fairly good coal, say, about 13,000 British thermal 

 units of energy, may be assumed as ample for the production of all the 

 work and power, and all the active phenomena, internal as well as 

 external, of the human machine, when doing a full day's work. 



This is 10,000,000 foot-pounds, nearly, of energy supplied. 



So far as now known, this food supply and the oxygen required for 

 its complete combustion, with some nitrogen and a minute quantity of 

 mineral matter, constitute the total intake of the animal machine, 

 except that a quart of water, more or less, is needed to dilute the cir- 

 culating fluids of the system. The next question for our examination 

 is: What amounts of energy are expended and utilized in the various 

 processes of the operation, of maintenance and repair, and of perform- 

 ance of external work, useful and useless, in an average day, with its 

 usual distribution of working time and rest? 



Scammel. Ibid., page 74. 



