96 DIGESTION 



of the quantity of heat provided by the food, it being assumed 

 by the principle of the conservation of energy that, although 

 it can be transformed, the original quantity of energy remains 

 constant. Physicists have chosen, to enable them to measure 

 a quantity of energy of any kind, a certain amount of heat 

 as a unit. This is known as a calorie, and a great Calorie is 

 that quantity of heat which is necessary to warm one kilo- 

 gramme of water from zero to one degree Centigrade. Heat 

 was chosen as the unit of measurement, for heat alone holds 

 a peculiar position in relation to other forms of energy. It 

 is the sole form into which all others can be completely trans- 

 formed. But it is now doubted whether complete transforma- 

 tion can take place even into heat. 



People who are interested in diet have found out how many 

 units of heat, called Calories, must be supplied by the food 

 in order to keep the animal in health. A three year old child 

 requires 1000 large Calories a day, a fourteen year old child 

 about 1800, a full grown man about 3000 to 3500 according 

 to the work he is doing, whilst a woman does quite comfortably 

 on 2100 calories. But you can have a theoretically ideal food 

 with the requisite number of Calories and yet, if it be unpalatable 

 or lacking in vitamins, you cannot induce people to eat it 

 or their bodies to assimilate it. Well-to-do people in civilized 

 nations generally eat too much, and they generally have 

 a mixed diet, whereas some of the Red Indians of North 

 America are almost wholly flesh-eaters ; the enormous popula- 

 tions of China, India and Japan are in the main vegetarian; 

 certain tribes in Central Africa live entirely on bananas; 

 Esquimaux live largely on blubber and on fish. But there is 

 little doubt that the more civilized and more progressive races 

 are omnivorous. The teeth and digestive tract of man are 

 characteristic of an omnivorous animal, and this is equally 

 true of bears. 



Appetite 



" You may take a horse to the water, but you cannot make 

 him drink." You may have a most scientifically prepared 

 food, containing the proper amount of Calories and an ade- 

 quate supply of vitamins, but, unless it is palatable, people 



