356 BIOLOGY FOR BEGINNERS 



phosphorus which ordinary fats do not. It is affected by alochol, 

 anaesthetics, and poisons and thus may be the means by which 

 these act upon the system. At all events it seems to be derived 

 from fat foods and is very essential to the nervous system. 



Vitamines. It has been found that a diet restricted to a few 

 foods, especially if they all be cooked, does not always result in 

 proper nourishment, even though the balance may seem to be cor- 

 rect. This has led to the belief that there are substances called 

 vitamines in certain foods, which are necessary to health and are 

 destroyed by cooking. In order to supply these, the diet should 

 include a moderate amount of uncooked foods, such as fruits, let- 

 tuce, celery, tomatoes, milk, and butter. 



Fruits and vegetables are important for another reason. They 

 produce alkaline substances when digested and these neutralize 

 harmful acids formed by the digestion of proteids. They are also 

 our chief source of iron and some other necessary mineral salts, 

 and cannot be safely omitted from the dietary, even though their 

 calorie value is not always very high. 



If energy alone was all that is required of food we could get our 

 2500 calories from about twenty ounces of sugar or white of egg, 

 or half that amount of clear butter. Both our instinct and ex- 

 perience teach us that this would not support a healthful 

 life. 



Dietary Diseases. Certain natives of Japan and the Philippines 

 live largely on rice. This supplies plenty of energy but lacks other 

 essential nutrients and they suffer from a disease called beri-beri, 

 which is quickly cured by a change of diet. Pellagra is a sickness 

 which occurs in our southern states, and seems to be caused by a 

 diet poor in proteid. Scurvy is another dietary disease, caused by 

 lack of fresh fruits and vegetables. It used to be common among 

 sailors whose long voyages forced them to live on salt meats with- 

 out any fresh foods, and was promptly relieved by use of fruit and 

 fruit juices when they came ashore. Long ago the sailing vessels 

 used to carry casks of lime juice to prevent this, and now it has 

 become a custom to refer to any sailor on a slow sailing vessel as 

 a " lime juicer." 



