Most people suppose the stomach finishes digestion, but it only initiates
the digestion of those foodstuffs which contain nitrogen, leaving fats,
starches and sugars untouched.

By an obscure process, the acid chyme stimulates the walls of the bowel to
send a chemical messenger, a Hormone through the blood to the liver and
pancreas, warning them their help is needed, whereupon they actively
secrete their ferments.

The secretion of the pancreas is very complex. It carries on the work of
the saliva, and also splits insoluble fats into a soluble milky emulsion.

Fats are unaffected in the mouth and stomach, which explains why hot,
buttered toast, and other hot, greasy dishes are so indigestible. The
butter on plain bread is quickly cleared off, and the bread attacked by the
gastric juice, but in toast or fatty dishes, the fat is intimately mixed
with other ingredients, none of which can properly be dealt with. Always
butter toast when cold.

To continue: The secretion of the pancreas also contains a very active
ferment, which, on entering the bowel, meets and mixes with another ferment
four times as powerful as gastric juice, which completes the digestion of
the proteids.

Meantime, the secretions of Lieberkühn's glands (of which there are immense
numbers in the small intestine) are further aiding the digestion of the
chyme, while the liver (the largest and most important gland in the body)
sends its ferments, and the gall-bladder its bile, which further emulsifies
the fatty acids and glycerin until they are ready to be absorbed.