A new pharmacology is rapidly developing. The physiological action of every substance likely to be of service as a drug is put to the proof. Having ascertained what is wrong, and knowing exactly what effects his drugs are capable of producing, the physician devises the adjustment which he may attempt without risk of making matters worse. He then seeks, if possible, a chemical messenger near akin to the messenger whom Nature herself would send; at least, this is the ambition of the modern pharmacologist. CHAPTER VI DIGESTION =The Canal.=—The prospect presented by a widely open mouth is too familiar to need description, but a few details may be pointed out. The teeth are, or should be, thirty-two in number. Starting from the middle line of either jaw, the two first are incisors, with chisel-shaped cutting edges. If they meet, as they ought to do, their edges are ground flat. The third tooth is the canine, with a more or less pyramidal crown. Then two premolars, or “milk-molars,” as they are often termed, because they are the only grinding teeth of the first dentition. Twenty is the full complement of teeth in a child. Lastly, three strong grinders—the molar teeth. The third molar, or wisdom-tooth, is evidently disappearing in the human race. In civilized people, whose brains are large and jaws small, it does not appear until about the twentieth year. Sometimes it tries to squeeze through the gum of a jaw not large enough to carry it, and causes trouble by becoming “impacted” beneath the ascending ramus. Not infrequently it fails to appear. It may be truly said that the increasing wisdom of the human race is responsible for the postponement of its development, although this is hardly the circumstance to which it owes its name. A fold of mucous membrane—the frenulum linguæ—connects the under side of the tongue with the floor of the mouth. On either side of this may be seen the opening of a duct common to the submaxillary and sublingual salivary glands. The opening of the duct of the parotid gland is not so easy to find. It pierces the mucous membrane of the cheek opposite to the base of the second molar tooth of the upper jaw. The parotid gland lies just below the ear, behind the jaw. The saliva which it secretes is a watery fluid containing little beside salt and a weak ferment. It serves to moisten the food as it is being crushed by the molar teeth. The submaxillary and sublingual secretions contain, in addition to the ferment, ptyalin, mucus which the tongue mixes with the masticated food as it forms it into a bolus suitable for swallowing. The dorsal surface of the tongue is covered by papillæ, which rasp the food against the palate. Of these the greater number are pointed, or filiform. The remainder are flat-topped, or fungiform. The two varieties may be distinguished with a lens, especially on the sides of the tongue. Usually the fungiform papillæ are the redder. In fever,