56 STUDIES IN PHYSIOLOGY 



possible, and the vegetables should be cooked rapidly, in 

 order to give less time for the solvent action to take place. 

 Bread Making. When bread is made, water (or milk), 

 butter, salt, sugar, and yeast are added to flour. After the 

 mixture has been stirred together, a sticky mass of dough is 

 formed, which in a warm place begins to rise. This is due 

 to the fact that the yeast cells change the sugar into alcohol 

 and carbon dioxid. Bubbles of gas are thus imprisoned in 

 the sticky dough. While expanding and seeking to escape, 

 they make the solid mass porous. After the bread has risen 

 sufficiently, it is kneaded in order to break up the large bub- 

 bles and in order to distribute the gas throughout the dough. 

 When the bread is baked, the alcohol and carbon dioxid pass 

 off into the air, leaving the bread light and digestible. 



6. DAILY DIET 



Diet required by Americans. Many investigations have 

 been carried on, in this country and in Europe, to determine 

 the amount of each kind of nutrient needed per day for the 

 work of the body. The conclusions that were drawn from 

 this study are represented on the lower two lines of Fig. 18. 

 According to these conclusions the average American, when 

 at moderate work, requires about one fourth of a pound of 

 proteids to provide for the growth and repair of the body, 

 and a quarter of a pound of fat and a pound of carbo- 

 hydrates to furnish the needed energy. This is about the 

 amount eaten by a man of average appetite. 



Recently, however, at the Scientific School of Yale Uni- 

 versity, some very careful experiments have been performed 

 by Professor Chittenden which seem to prove conclusively 

 that this pound and a half of solid nutrients for each day is 

 considerably more than what the body really needs. Dr. Chit- 

 tenden experimented on five of the Yale University profes- 

 sors, on thirteen soldiers of the United States army, and on 

 five of the best athletes at Yale ; he found that all agreed 

 they could do better physical and mental work, and that, too, 



