140 FOODS 



The Right Quantity is Important. Our second ideal requirement is that 

 the quantity of the food should be sufficient for the normal needs of the 

 organism, but not excessive. This is well-nigh axiomatic, and yet its 

 scientific meaning demands expression and the average limits of a normal 

 diet, maximal and minimal, require some discussion. If a diet be too 

 small in amount, short of fasting or its continuance into starvation, the 

 consequences are a diminution both of tissue-repair and of the energy 

 of the body. The organism which is living or has lived on its own tissue- 

 fat to help meet the deficiency of income shows that bony angularity 

 most of us are familiar with, unfortunately, sooner or later, in all localities. 

 The individual is obviously weak, and exertion, either physical or mental, 

 requires an unusual effort. The deficiency in heat-production is felt in 

 cold weather in that sense of continual chill to which very poor folk 

 strive in vain to become used, the thermometer showing perhaps half 

 a degree's depression of the body-temperature. 



The determination of the quantity of food in an average diet has been 

 and is a matter of much research and of more discussion. The explana- 

 tion of this indeterminateness is to be found in the very widely differing 

 needs and habits of the classes and divisions of mankind. Physiology has 

 been heretofore very largely a descriptive science, analyzing and system- 

 atizing what it finds in Nature, and only gradually is it becoming a nor- 

 mative science which sets ideals or tells what ought to be. In this case, 

 therefore, we can but describe what people actually do eat, and if the 

 science declares what men should eat, how their diets ought to be com- 

 posed, it will be only by taking as a basis the best average of actual 

 diets used by any class of persons that can be arrived at. It is only the 

 faddists and the "cranks" who, on any other basis than this which is 

 natural and actual, say what men should eat. Still, of late, quantitative 

 researches have been made by methods soon to be described, which, in- 

 dependently of actual dietary conditions, have more or less well estab- 

 lished the proper amount of food for persons under various circum- 

 stances of metabolic expenditure, climate, etc. To a great extent these 

 experimental products and the data derived from observations of actual 

 corresponding diets very closely agree in all essential respects. It is 

 agreements of this sort which give encouragement in the often slow 

 progress of a science. 



THE ENERGY-VALUES OF FOODS. The quantitative work referred 

 to has been accomplished by a method of accurate measurements of the 

 energy-values of nutrients in relation to the income and expenditure of 

 energy by animal organism. This method is termed calorimetry, literally 

 "heat-measurement," for the process was developed in studying animal 

 heat, its sources and modes of loss. At the present time calorimetry 

 means the accurate measurement of the energy-values of the ingesta of 

 organisms, oftentimes in relation to the heating-energy and the moving- 

 energy of the organisms. In its theory it is a simple method, for it merely 

 attempts to measure the income and expenditure of animals (and 

 latterly of plants sometimes) and to determine the combustion-value 



