176 How a Complex Animal Uses Food 



iron. Iodine, which is needed to prevent 

 goiter, is best obtained from fish and 

 other sea food. To review this informa- 

 tion do Exercise 7. 



Water is still another substance needed 

 by the body. To begin with, it helps in 

 assimilation. Then, too, it helps in dis- 

 solving substances so that thev can move 

 around by the process of diffusion. You 

 should drink a considerable amount of 

 water each day. 



What else is needed in the diet? Foods 

 contain proteins, carbohydrates, fats, 

 minerals, and water; but they contain 

 other useful substances too. They have 

 minute amounts of many different com- 

 pounds which add flavor. These add to 

 your enjoyment of food. And foods that 

 come from plants have more or less cellu- 

 lose and woody substances making up 

 the walls of each cell. Potato skins are 

 made up largely of such materials. While 

 you obtain little nourishment from them 

 they are of considerable importance in 

 your diet. These substances are called 

 roughage. A certain amount of roughage 

 is valuable for making the intestines push 

 the food along. You will understand this 

 better when you have studied digestion. 



But besides the flavoring and roughage, 

 foods contain still other compounds 

 which are not used directly in making 

 protoplasm or in oxidation. Yet, they are 

 necessary to v^ou. These substances are 

 the vitami?is (vye'te-mins). They were 

 discovered in the course of experiments 

 on diseases which had puzzled people for 

 centuries. There were mysterious out- 

 breaks of disease which seemed to have 

 something to do with diet. Only within 

 the last fifty years have these mysteries 

 been definitely cleared up. 



UNIT IV 



Fig. 195 The smaller guinea pig has scurvy. 

 What must have been lacking in its diet? (u. s. 



DEPARTMENT OF AGRICULTURE) 



Mysterious diseases caused by faulty 

 diet. In the dark ages men told of a serious 

 disease which sooner or later attacked 

 sailors on long voyages. Their muscles 

 ached, they became weaker and weaker, 

 and blood flowed from their noses. Often 

 they died. The disease was called scurvy. 

 No one knew whether they were poi- 

 soned by their food, which consisted 

 principally of salted meat and dry crack- 

 ers, or grew sick from long exposure to 

 the sea air. It was noted in England in the 

 eighteenth century that if sailors drank 

 the juice of lemons or limes, they did not 

 suffer from scurvy. The reason was not 

 understood. But to prevent further out- 

 breaks of the disease a law was passed in 

 England more than a century ago requir- 

 ing that a supply of lemons or limes be 

 taken on long voyages. This is why Eng- 

 lish sailors are called limeys. 



Somewhat later the Japanese had simi- 

 lar disastrous experiences with another 

 disease, outbreaks of which occurred i/ 



