vitamin tablets in addition to the regular rationed diets, and equal numbers 

 had only the regular diets. Height, weight, and sickness records showed 

 no difference whatever between the two groups. A suitable diet needs no 

 supplement; a diet that is not suitable should be replaced with one that is. 



In Brief 



Body-building, energy-yielding, and regulative nutrients are essential to 

 all living protoplasm. 



Proteins, the nitrogen-containing nutrients, serve both as protoplasm- 

 building and as energy-yielding material. 



Fats and carbohydrates supply energy only. 



Certain chemical elements are indispensable to protoplasm; if soils or 

 food lack any of these, the growth of living organisms is limited. 



Several minerals are essential to the growth activities of many kinds of 

 protoplasm; some minerals are used in the formation of special tissues, 

 such as bones or shells. 



Some of the mineral substances found in cells are probably waste prod- 

 ucts; others may be injurious substances separated out of the protoplasm. 



Normal development of living organisms depends upon the presence in 

 the diet of minute traces of certain "regulative" substances. 



Vitamins have been associated with extremely abnormal symptoms de- 

 veloped by organisms entirely deprived of them, and have received anti- 

 names. Moderate deficiency is more common, and has been widely 

 remedied by supplying adequate amounts of the various vitamins. 



The ultimate sources of vitamins are plants. 



Present knowledge indicates that with a little care adequate amounts of 

 all the vitamins can be obtained in natural foods, so that we do not gen- 

 erally have to depend upon the drugstore for these substances. 



As we come to know the specific composition of vitamins, we can use 

 chemical tests for their presence in foods instead of tests on experimental 

 animals. 



EXPLORATIONS AND PROJECTS 



1 To find the effect of a diet deficient in energy, feed two rats three to four 

 weeks of age all they will eat of the complete diet given in footnote 2, p. 112, and 

 feed two other rats just j as much of the same diet in proportion to their weight. 

 About 0.12 gram per gram of rat per day should hold their weight nearly constant. 

 At the end of four or five weeks, give the low-energy animals all the food they 

 will eat and see whether they catch up with the control animals. Record and 

 graph daily weights; interpret results. 



Ill 



