500 THE HUMAN BODY 



Therefore the fats are shunted into another course which carries 

 them into the blood stream without having first to traverse the liver. 



Absorption from the Large Intestine. The mass that passes 

 through the ileocolic valve into the large intestine contains com- 

 paratively little absorbable food material. The carbohydrates and 

 fats are very completely removed during the passage of the small 

 intestine, and fully ninety per cent of the proteins as well. There 

 remains for the large intestine, then, only the absorption of the 

 protein residue and the absorption of water. It is probable that 

 this latter function, that of absorbing water, is in reality the chief 

 one possessed by the large intestine. There is virtually no ab- 

 sorption of water in the small intestine; the intestinal contents 

 pass the ileocolic valve as liquid as when leaving the stomach. 

 This maintenance of a liquid consistency is, of course, essential to 

 the absorptive processes, and it is only after all absorbable food 

 has been removed that the water, which is also needed by the 

 Body, is taken up. 



The Food Requirement of the Body. If we know how much 

 energy the Body liberates in a day, and how much tissue break- 

 down it suffers, we ought to be able to estimate how much energy- 

 yielding food, and how much tissue-repair food is required daily; 

 assuming, of course, that we know the amount of energy yielded 

 by definite weights of food stuffs. By the use of devices called 

 calorimeters the total energy liberation of the Body per day has 

 been determined under various conditions, and the energy content 

 of the various foods has also been found. We learned in a previous 

 chapter (p. 107) that a unit of heat energy commonly used in 

 physiology is the Calorie; the amount of heat required to raise 

 1,000 grams of water through 1 centigrade. In terms of this 

 unit the energy output of man in 24 hours averages from about 

 2,400 Calories for men of sedentary occupation to 5,000 Calories 

 for those doing heavy manual labor. The energy yield of the 

 various foods is as follows: 



Carbohydrates 4. 1 C. per gram. 



Proteins 4. 1 C. " " 



Fats 9.3C. " " 



It is therefore a matter of simple calculation to determine how 

 much of any one food stuff is needed to supply the required en- 



