Milk is the natural food of the mammalian young, each species producing milk peculiarly and precisely adapted to the various needs of its own young. It is the rule that the young take the milk alone, not in combination with other foods. Milo Hastings once objected that calves will take milk and a few minutes later eat grass. But we are not to forget that the calf has a few more stomachs than we have and can do this without difficulty.
Milk acts as a gastric insulator. Its cream inhibits the outpouring of gastric juice for some time after the meal is eaten. Milk does not digest in the stomach, but in the duodenum, hence in the presence of milk the stomach does not respond with its secretion. This prevents the digestion of other foods introduced along with the milk. Perhaps milk could be taken with starch, if we took pure starch, but no starch food is pure starch. The use of acid fruits with milk does not cause any trouble and apparently does not conflict with its digestion.