The reference to Chios, an island in the Grecian Archipelago, is presumably for the purpose of indicating the character of the ‘gum.’ The Chios ‘gum’ of the ancients has been described as an earth of a compact character, probably argillaceous, and had the reputation of possessing medicinal qualities. Its consistency and appearance may have been such as to have led to its being popularly called ‘gum.’ That the chewing of gum, or some other article or waxy substance suitable for chewing, was in vogue at the time, there can be no doubt, and that the discovery of such a substance would be regarded as an important acquisition is implied by its being specially mentioned and promised by Columbus. Years ago, more than half a century, shoemakers’ wax, so-called, Burgundy pitch and crude spruce-gum were chewed to a considerable extent, as the writer clearly remembers. Betel chewing, the leaves and the nut mixed in certain proportions _with lime_, as practiced in Asiatic countries, naturally occurs to the mind in connection with the foregoing, as well as occasional instances of chewing slate pencils and lime mortar, an interesting case of the latter having been brought to my notice several years since by a well-known physician of Newark, N. J. But these are rather exceptional and individual cases, therefore not to be regarded as general or popular habits. From the _chewing_ of earthy substances to the _eating_ of the same, would appear to be but a natural step. The latter habit, so far as facts are available, is of comparatively infrequent occurrence and restricted to a much smaller number of persons. Beds of white infusorial earth, resembling magnesia in appearance, known as _Bergmehl_, occur in Lapland and Finland. This is, or has been used in seasons of scarcity, mixed with flour made of some kind of grain or ground birch-bark, and _clay-eating_ probably, to a greater or less extent, still continues to be a habit in North Carolina as in the past. The effect of this habit, as any intelligent person would suppose, is decidedly injurious to the individual that pursues it. In several cases that have come under my observation the results are exhibited in sallowness of complexion, lack-lustre eyes, distension of the abdomen caused by engorgement or clogging of the liver, and other intestinal derangement, listlessness and general debility. ROB’T E. C. STEARNS. _Los Angeles, Cal._ SCIENTIFIC LITERATURE. _A GRAMMAR OF SCIENCE._