The teeth perform the very important function of breaking down our food and enabling it to be intimately incorporated with the saliva and afterwards with the digestive juices.  The Anglo-Saxon race shows a greater tendency to degeneracy in the teeth than do other races; the teeth of the present generation are less perfect than those of previous generations.  A dentist writes (Lancet, 1903-2, p. 1054) “I have had the opportunity of examining the teeth of many natives in their more or less uncivilised state, from the Red Indians of North America, the negroes of Africa, to the more civilised Chinese, Japanese, and Indians of the East, and I have usually found them possessed of sound teeth, but so soon as they come under the influence of civilised life in Washington, Montreal, London, Paris and other cities, their teeth begin to degenerate, though their general health may remain good.”  In a long article on mastication in the Lancet (1903-2, p. 84) from which we have already quoted, Dr. Harry Campbell gives as the effect of thorough and efficient mastication, that it increases the amount of alkaline saliva passing into the stomach, and prolongs the period of starch digestion within that organ.  That it influences the stomach reflexly by promoting the flow of gastric juice.  That the frequent use of the jaws and the tongue, during the period of growth, cause the jaws to expand.  If the jaws are not adequately exercised during this period, owing to the use of soft food, they do not reach their normal size, the teeth are overcrowded, do not develop fully, and are prone to decay.  The effect of vigorous mastication is to stimulate the circulation in the tooth pulp, which promotes nutrition and maintains a firm dental setting.  Dr. Campbell writes:  “I am perfectly at one with Dr. Wallace, in believing that the removal of the fibrous portion of food is the main cause of the prevalence of caries among moderns.”

When the food reaches the stomach, gastric juice is secreted.  This juice contains a ferment called pepsin and hydrochloric acid.  Pepsin is only active in an acid media.  Starch digestion proceeds in the stomach to such a time—­stated as from 15 to 30 minutes—­when the acid gastric juice has been poured out in sufficient quantity to neutralise the alkalinity of the saliva.  The gastric juice acts upon the proteids only.  After a time the liquefied contents of the stomach are passed into the first portion of the small intestine, called the duodenum.  Here it meets with the pancreatic juice, which like the gastric juice attacks proteids, but even more energetically, and only in an alkaline media.  The proteolitic ferment is called trypsin.  The pancreatic, the most important of the digestive fluids, contains other ferments; one called amylopsin, takes up the digestion of any remaining or imperfectly converted starch left from the salivary digestion.  Amylopsin is much more powerful and rapid than the ptyalin of the saliva, especially on uncooked starch.