THE INTAKE OF MATERIALS AND ENERGY 63 



body temperatures. The other inorganic materials essential to the body- 

 include chlorides, sulphates, and phosphates of calcium, sodium, potas- 

 sium, iron, magnesium, and zinc. Iodine is a constituent of thyroxin, one 

 of the hormones to be discussed later; minute amounts of copper, man- 

 ganese, cobalt, and bromine are also needed. 



Diet 



The sum of the food materials taken in by an animal over a specified 

 period of time makes up its diet. As we have already seen, the diet must 

 include materials to be burned as fuel for the release of energy; materials 

 for building and repairing cells; inorganic materials to be used as struc- 

 tural elements, as solvents, as cooling agents, or for other purposes; and 

 certain special substances (the vitamins) required for the proper func- 

 tioning of the organism. 



For an animal simply to eat until its hunger is satisfied is no guarantee 

 that all these dietary requirements will be met. Cattle in southern Florida, 

 eating their fill of the lush pasturage, fell victims by the thousands to a 

 disease called "salt-sick." They were actually starved for certain minerals 

 lacking in the soil, and hence in the plants which formed their food. By 

 supplying these minerals in salt blocks or by other means the cattle were 

 restored to health. Man, omnivorous in his food habits, would seem much 

 less likely to suffer from dietary deficiencies, but actually, from ignorance 

 or necessity, he very often does so. It will be of interest to consider briefly 

 the kinds and amounts of food that are required adequately to maintain 

 the human body under various circumstances. 



An ordinarily active man weighing 150 pounds needs enough food to 

 yield approximately 3900 Calories 1 of heat per day. If he is engaged in 

 hard physical work the Calorie requirements may be as great as 5000 or 

 even 6000 per day. Obviously the age, sex, weight, and activity of an 

 individual, as well as the climate in which he lives, enter into a determina- 

 tion of his Calorie requirements. A two-year-old child may need only 900 

 Calories per day; the average woman needs about 2100. 



In addition to the fats and carbohydrates that are the chief energy- 

 furnishing foods, the diet must include proteins, essential minerals, and 

 vitamins. The proteins, as previously mentioned, yield amino acids for 

 building the new proteins needed by the cells for growth and repair. Of 

 the 23 amino acids known, 10 are believed indispensable for human 

 metabolism, and the diet must include protein foods from which these 

 particular amino acids may be derived. At least 8 of the approximately 



1 "Calorie," spelled with a capital letter, is the great calorie — the amount of heat 

 required to raise the temperature of 1,000 grams (1 liter) of water 1°C. The small 

 calorie, written without a capital letter, is Kooo of the great calorie. 



