“Now that reminds me of a circumstance that took place in a neighborhood where I lived when I was a boy. In the spring of the year the farmers were very fond of the dish which they called greens, though the fashionable name for it nowadays is spinach, I believe. One day after dinner, a large family were taken very ill. The doctor was called in, who attributed it to the greens of which all had freely partaken. Living in the family was a half-witted boy named Jake. On a subsequent occasion, when greens had been gathered for dinner, the head of the house said: ‘Now, boys, before running any further risk in this thing, we will first try them on Jake. If he stands it, we are all right.’ And just so, I suppose,’ said Mr. Lincoln, ‘Congress thought of the State Banks.'”
Francis Carpenter, Six Months at the White House, p 53-54.