Taste, however, is not equally distributed over the whole surface of the tongue alike.  There are three distinct regions or tracts, each of which has to perform its own special office and function.  The tip of the tongue is concerned mainly with pungent and acrid tastes; the middle portion is sensitive chiefly to sweets and bitters; while the back or lower portion confines itself almost entirely to the flavours of roast meats, butter, oils, and other rich or fatty substances.  There are very good reasons for this subdivision of faculties in the tongue, the object being, as it were, to make each piece of food undergo three separate examinations (like ‘smalls,’ ‘mods,’ and ‘greats’ at Oxford), which must be successively passed before it is admitted into full participation in the human economy.  The first examination, as we shall shortly see, gets rid at once of substances which would be actively and immediately destructive to the very tissues of the mouth and body; the second discriminates between poisonous and chemically harmless food-stuffs; and the third merely decides the minor question whether the particular food is likely to prove then and there wholesome or indigestible to the particular person.  The sense of taste proceeds, in fact, upon the principle of gradual selection and elimination; it refuses first what is positively destructive, next what is more remotely deleterious, and finally what is only undesirable or over-luscious.

When we want to assure ourselves, by means of taste, about any unknown object—­say a lump of some white stuff, which may be crystal, or glass, or alum, or borax, or quartz, or rock-salt—­we put the tip of the tongue against it gingerly.  If it begins to burn us, we draw it away more or less rapidly with an accompaniment in language strictly dependent upon our personal habits and manners.  The test we thus occasionally apply, even in the civilised adult state, to unknown bodies is one that is being applied every day and all day long by children and savages.  Unsophisticated humanity is constantly putting everything it sees up to its mouth in a frank spirit of experimental inquiry as to its gustatory properties.  In civilised life we find everything ready labelled and assorted for us; we comparatively seldom require to roll the contents of a suspicious bottle (in very small quantities) doubtfully upon the tongue in order to discover whether it is pale sherry or Chili vinegar, Dublin stout or mushroom ketchup.  But in the savage state, from which, geologically and biologically speaking, we have only just emerged, bottles and labels do not exist.  Primitive man, therefore, in his sweet simplicity, has only two modes open before him for deciding whether the things he finds are or are not strictly edible.  The first thing he does is to sniff at them; and smell, being, as Mr. Herbert Spencer has well put it, an anticipatory taste, generally gives him some idea of what the thing is likely to prove.  The second thing he does is to pop it into his mouth, and proceed practically to examine its further characteristics.