334 HUMAN PHYSIOLOGY 



the consumption of fuel. It is, in effect, the demon- 

 stration that the body is strictly subject to the principle 

 of the conservation of energy. An alcohol lamp can 

 be substituted for a man and the calculations of direct 

 and indirect calorimetry carried out upon it with parallel 

 results. If we had found that a man could produce 3000 

 Calories when his fuel consumption entitled him to only 

 2000 we should have concluded that the living state con- 

 ferred upon matter the ability to create as well as to 

 transform energy. 



The fact is to be pressed home that we can judge of 

 the metabolism with great accuracy by analyzing the 

 excreta but not by fixing our attention upon the day's 

 ration. There is a presumption that the food will 

 correspond in quantity and proportion with the material 

 metabolized but this is only a presumption. We have 

 only to consider that the income may be nil and the 

 metabolism large, as when a starving fisherman rows 

 for his life. Over long periods there must, of course, 

 be an approximation of the diet to the metabolism. 

 The observation that the daily ration of a Maine lumber- 

 man has a value of 7000 Calories or more is a fair indi- 

 cation that the output of energy is of the same order, 

 but we cannot assume a close correspondence upon a 

 single day. 



There have been many studies of the diets chosen by 

 various classes of people. Men who do hard work 

 commonly secure a supply of 3500 Calories or there- 

 abouts. This is the figure for farmers in widely sepa- 

 rated countries. The ration of sedentary individuals 

 may be 2500 Calories or even less. Advocates of low 

 feeding have urged that these allowances are too liberal 

 and may be reduced with advantage by 500 Calories 

 or so. It does not appear that many people have de- 

 parted greatly from the average practice of the race, 

 unless for rather short periods. We shall refer to this 

 question again. 



When we speak of the calorific value of a ration we 



