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.
The chemically-changed chyme is now termed Chyle, and is ready to be absorbed by the minute, projecting Villi.
The fatty portion of the chyle is absorbed by minute capillaries and ultimately mingles with the blood, which may look quite milky after a fatty meal.
The remaining food is absorbed by the blood capillaries in the villi, and passes to the liver for filtration and storage.
The large bowel has Lieberkühn's glands, but not villi, and is relatively unimportant, though most of the water the body needs is absorbed from here.
How food becomes energy and tissue we do not know. The tissues are continually being built up from assimilated food, and as constantly being burnt away, oxygen for this purpose being extracted from the air we inhale, and carried via the blood to every corner of the body. The ashes of this burning are expelled into the blood and lymph, and carried out of the body by the kidneys, lungs, skin and bowels. The product of the burning is the marvel--Life; the extinction of the fire is the terror--Death.