FOOD 419 



Food. Experiment 138. Chop a piece of the white of a hard- 

 boiled egg into pieces about as large as the head of a pin and place 

 in a test tube. Chop up another piece much finer than this and 

 place it in a second test tube. Make a mixture of 100 cc. of water, 

 5 cc. of essence of pepsin, and 2 cc. of hydrochloric acid. Pour into 

 each test tube enough of this mixture to cover the white of egg to 

 a considerable depth. Shake thoroughly and put in a place where 

 the temperature can be maintained at 37 C. or 98 F. A fireless 

 cooker or a bucket of warm water is good for this. Allow to stand 

 for several hours, keeping the temperature constant. The white 

 of egg is dissolved, the action being more rapid in the second tube. 

 Try the same experiment using water; using dilute hydrochloric 

 acid. Do these have the same effect as when used with the pepsin? 

 The pepsin solution is an artificial gastric juice. 



In order that the work of the body may be carried on, 

 food is required. This food may be supplied by either 

 animals or plants. The original source of all animal and 

 plant food, as has been seen, is in the chlorophyll manu- 

 factory of the leaf and green stem. After this leaf food 

 has been manufactured, it is simply modified by the plants 

 and animals through which it passes. The food is used 

 (1) in growing new cells, (2) in repairing cells that have 

 been used up or destroyed, (3) in providing energy to carry 

 on the activities of the body and maintain its heat, or (4) in 

 doing external work, such as moving the body itself from 

 place to place or moving other bodies. 



To furnish any of this energy, the cells must be able to 

 combine food with oxygen. To do this the food must be 

 digested or prepared so that it can pass through animal 

 tissue. In the higher animals, a complicated apparatus is 

 provided to accomplish this. In man it is briefly as follows : 

 a long, continuous tube, the food-tract or the alimentary 

 canal (Figure 135) extends through the body. Different 



