THE DIGESTIVE SYSTEM 



469 



remote from the sea, the iodine is not suf- 

 ficient for an adequate diet and must there- 

 fore be supplemented. 



While sodium chloride (table salt — 

 NaCl ) is probably adequate in most meats, 

 it is less abundant in plant products; for 

 that reason, food is usually salted during 

 cooking and the salt shaker forever adorns 

 the table, just in case. Salt is essential for 

 normal body maintenance. Hydrochloric 

 acid, for example, is produced in the cells 

 of the stomach, using the CI from the 

 NaCl. With severe sweatino; there is a 

 gradual loss of salts, and if prolonged will 

 result in "miner's cramps," where large 

 muscles go into painful spasms. The victim 

 suffers from extreme thirst but the more 

 water that is taken the more severe the 

 spasms, because the salt loss is proportional 

 to the water loss. During the recent war 

 where so much work was done in the 

 tropics, it was found that by eating salt 

 tablets the symptoms could be avoided. 



Since the body is primarily water and 

 since approximately 2000 cc. are normally 

 lost each day, it follows that this important 

 substance must also be replaced continu- 

 ously. One can survive many weeks without 

 food but only a few days without water. 



In addition to minerals and water, the 

 protoplasm-building proteins must be pres- 

 ent in the diet in considerable quantities. 

 Larger amounts of protein are essential for 

 the growing body than the 50 grams per 

 day required by the adult. This amount 

 must include all of the amino acids ( about 

 10 ) that the human body cannot synthesize 

 from simpler compounds. These are the 

 so-called "essential amino acids." There are 

 many others that can be manufactured by 

 the intracellular enzymes, providing the 

 raw materials are available. Some proteins, 

 such as those derived from milk, meat, 

 eggs, and wheat, contain all of the essential 

 amino acids, whereas others, such as those 

 from gelatin and corn, lack one or more. A 

 diet including only one of these two pro- 

 teins would be inadequate. It is therefore 



best to eat a variety of proteins in order 

 that all of the amino acids be supplied in 

 sufficient quantity for proper growth and 

 repair. 



Foods for energy 



All of the energy utilized by the body 

 must come from the food brought into it. 

 Very little energy is derived from breaking 

 the large molecules of protein, carbohy- 

 drate, and fat down to absorbable size dur- 

 ing digestion. The bulk of the energy comes 

 from further breakdown by oxidation of 

 these absorbed products in the cells. When 

 carbohydrates, fats, and proteins are burned 

 to the same end products, either in the 

 body or artificially outside the body, they 

 deliver the following numbers of calories 

 per gram: proteins and carbohydrates — 

 about 4 calories; fats — about 9 calories. As 

 far as energy requirements are concerned, 

 one food is as good as another. Carbohy- 

 drates, of course, burn readily to supply 

 energy. One can also derive all required 

 energy from protein alone by conversion 

 of a part of it (about 40 per cent) to glu- 

 cose and burning it. With fats the situation 

 is different. For some reason, when over 50 

 per cent of the caloric intake is fat, oxida- 

 tion is impaired, and fats burn best when 

 there is an adequate amount of carbohy- 

 drate present in the tissues. 



Accessory foods— the vitamins 



The discovery of vitamins has a long and 

 fascinating history. When man first began 

 to isolate himself from natural fresh foods 

 and to live on stored or dried foods the 

 "deficiency diseases" made their appear- 

 ance. Among the many diseases that ap- 

 peared, scurvy was the best known, and the 

 first for which a remedy was worked out. 

 That was some 350 years ago, long before 

 anybody knew anything about vitamins, or 

 much else concerning nutrition. A British 

 navy captain discovered that when his men 

 were down with scurvy after many months 

 at sea, their fresh foods exhausted, they 



