This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
Bread may be unfit for use from being made of adulterated or too old flour, from turning sour from bad flour developing excess of lactic acid, from becoming bitter from yeast, from becoming sodden from insufficient fermentation or aeration, and it may grow mouldy from exposure to air when it is too moist.
"Most of the diseases of the War of 1812 were due to defective food, and in 90 per cent of the cases the flour was at fault. In the War of the Rebellion similar reports were often received " (Woodruff).