11 



diet is essential to the maintenance of health. Before this fact was known 

 repeated efforts were made to supply only highly concentrated food to explorers 

 or to armies on the march, and 



MUCH SURPRISE 'WAS EXCITED 



at the disappointing results of the experiments. By degrees these were 

 traced to the detrimental effects of insufficient bulk in the food consumed. 

 This desirable element is furnished by the carbohydrate foods, a fact which 

 will be further explained a little later on. 



A very natural question at this stage will be: How has accurate knowl- 

 edge been gained of just 



WHAT SERVICE THESE CLASSES OF FOODS RENDER TO THE BODY? 



The part played by these foodstuffs in the nutrition of the body has been 

 quite gradually discovered by close observation and by scientific methods of 

 various kinds, so that to-day, when it is desired to understand accurately the 

 particular worth of any form of food, it is submitted to 



FOUR DIFFERENT KINDS OF TESTS, 



known respectively as: (1) The chemical; (2) the physical; (3) the 

 physiological; and (4) the economic. 



(1.) Chemical tests for food-value are designed to discover the exact 

 amount of each nutritive constituent a food contains. The bread, meat, 

 cheese, or other substance is subjected to certain processes which enable the 

 trained worker to separate out the protein or fat or carbohydrate or mineral 

 matters present, no matter how minute a proportion they may form 

 of the whole. In the early days of these chemical investigations into food- 

 values the interesting fact was discovered that similar constituents to those 

 in man's chosen foods are present in his body, not, of course, in the form 

 familiar to the naked eye; for the food eaten has to pass through many 

 changes during the intricate process of digestion before it can be carried by 

 the blood and lymph to the bones, muscles, nerves, and various organs the 

 structure of which it maintains. 



Fig. (1) gives an idea of the relative amount of each of these five 

 classes of substances which are found in the full-grown body ; naturally not 

 massed together as in the illustration, but dispersed in varying amounts and 

 proportions and forms in the different tissues. 



Obviously, therefore, it is a matter of importance to supply the right 

 amount of each substance by means of our daily diet, in order to maintain 

 their relative proportions in the body. Too much protein or too little fat 

 might conceivably disturb the balance of health. That is just 



THE LESSON MAN IS LEARNING AT SOME COST 



and by slow degrees. An excess of protein does not mean an increase of 

 strength or a finer body. Rather it results in disordered nutrition instead 

 of growth; in debility and dyspepsia instead of strength; and if there be 

 too little fat in the diet the deficiency is associated with 



MANY FORMS OF ILL-HEALTH; 



a tendency to " take cold," or to contract tuberculosis, or to suffer from 

 constipation ; to name but a few of the results now known to follow an 



