114 THE HUMAN BODY. 



which is carried in the blood all over the body to supply al- 

 buminous material to the tissues, is, for example, insoluble 

 in pure water, but dissolves readily if a small quantity of 

 common salt be present. Besides such uses, the non-oxidiz- 

 able foods have probably others, as what may be called 

 machinery formers. In the lime salts, which give their 

 hardness to the bones and teeth, we have an example of such 

 an employment of them; and to a less extent the same may 

 be true of other tissues. The body is a self-building and 

 self -repairing machine, and the material for this building 

 and repair, as well as the fuel or oxidizable foods which 

 yield the energy the machine expends, must be supplied in 

 the food. While experience shows us that even for 

 machinery construction oxidizable matters are largely 

 needed, it is nevertheless a gain to replace such substances 

 by non-oxidizable material when possible; just as, if prac- 

 ticable, it would be advantageous to construct an engine 

 out of a substance which would not rust, although other 

 conditions determine the selection of iron for building the 

 greater part of it. 



Definition of Foods. Foods are (I) substances which are 

 taken into the alimentary canal, which can be absorbed 

 from it, and after absorption serve to supply material for 

 the growth of the body, or for the -replacement of matter 

 which has been removed from it; or (2) they are substances 

 which can be oxidized in the body to yield energy for its use; 

 or (3) substances, which by dissolving nutritive or waste 



Illustrate the use of common salt in helping to keep important 

 substances in solution. Illustrate the employment of nou-oxidizable 

 foods in constructing the body. What must foods supply to the 

 body besides fuel? Why? Are oxidizable foods used in machinery 

 construction? Give an example showing the gain of using non- 

 oxidizable matters when possible. 



Give a definition of foods. 



