BIOLOGY IN HUMAN AFFAIRS 



gram of protein would provide about four calories, as 

 would also one gram of carbohydrates. However, one 

 gram of fat, which is more productive of energy than pro- 

 tein or carbohydrate, provides nine calories. It may there- 

 fore be seen how small a quantity of food is necessary to 

 produce four calories and why it is that butter and fats 

 help to put on weight so rapidly. Naturally, a person 

 doing a small amount of work does not need to take in 

 so many calories as one doing heavy labor. Whereas a 

 clerical worker eats from 2,500 to 3,000 calories per day, 

 a stevedore or woodchopper consumes from 4,500 to 6,000, 

 and a lumberman may take as much as 8,000. In the same 

 way, a seamstress takes from 2,000 to 2,300 calories, 

 whereas a maid-of-all-work or a laundress consumes 2,800 

 to 3,500. 



End Products of Digestion. Although much is known as to 

 what happens to the foods when taken into the body, 

 many additional investigations must be made before the 

 complete story of the digestive chemistry is told. 



Proteins break down into amino-acids and are circulated 

 in the blood in this form. Some of these products are 

 again put together to make body proteins, later to be 

 broken down a second time under the influence of various 

 conditions in health and disease. Some of the protein is 

 changed into urea and can be found in the urine in this 

 form. In certain diseases some of the products of digestion 

 and body chemistry, which ordinarily are changed for 

 various purposes within the body, are excreted unchanged; 

 and these have been studied by the physiological chemist. 

 By such studies it has been found, for example, that there 

 are forms of sugar which may be excreted and which will 

 give all of the ordinary tests for sugar, and yet prove not 

 to be the particular sugar which is associated with diabetes. 



A certain amount of various solutions is regularly found 

 in the urine; but under certain conditions of disease, these 



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