The composition and manufacture of bread are subjects which have been given much study. The carbon dioxide which serves to lighten the dough raised with yeast is produced at the expense of some of the starch of the flour. This starch is completely driven from the loaf as carbon dioxide gas and alcohol during the baking. The loss is estimated at about 2 per cent. Attempts have been made in large bakeries to save the alcohol, but no economical method has been devised. About fifty years ago, German chemists- in studying the question estimated that the food materials lost in twenty-four hours, when bread is raised with yeast, was sufficient to supply bread to 400,000 people! These figures were certainly startling to the thrifty Germans, and the possibility of producing the carbon dioxide gas in some less extravagant manner was studied with considerable care in German laboratories, and also at Harvard University in America. Baking powders are the result of these investigations. Gluten is not changed chemically by the action of the yeast or of the carbon dioxide, but it is physically changed - the escape of the gases stretching it out into fibres. Gluten, like other proteids, hardens when heated. Baking thus makes the porous condition of the dough permanent.