1. _Suitable Substances_ are, 1, All remedies which operate in small doses, as _Metallic Salts_; and 2, Those which are designed to act slowly and gradually, as certain _Alterative Medicines_, or 3, which are too easily soluble when exhibited in other forms, as _Gamboge_, &c. 4, Substances which are not intended to act until they reach the larger intestines, as in pills for habitual costiveness; _see Aloes_. 5, Bodies whose specific gravities are too considerable to allow their suspension in aqueous vehicles. _Efflorescent_ salts may also be exhibited in this form, but they ought to be first deprived of their water of crystallization, or the pills composed of them will crumble into powder as they dry. 2. _Unsuitable Substances_ are, 1, Those which operate only in large doses. 2, Which deliquesce. 3, Whose consistence is such as to require a very large proportion of dry powders to afford them a suitable tenacity, as _oils, balsams_, &c. 4, Substances that are so extremely insoluble, that when exhibited in a solid form they pass through the canal unaltered, as certain _extracts_. Many remedies which are incompatible with each other in solution, may be combined in pills, unless indeed their medicinal powers are adverse or inconsistent, or their divellent affinities sufficiently powerful to overcome their state of aggregation. II. THEIR FORMATION INTO MASSES. This is a subject of far greater importance than is usually assigned to it, as will be more fully explained in the sequel. 1. Many substances, as _vegetable extracts_, may be formed into pills without any addition; others, as _gum resins_, become sufficiently soft by being beaten, or by the addition of a drop or two of spirit, or _liquor potassæ_. Some dry substances react upon each other, and produce, without the addition of any foreign matter, soft and appropriate masses. The _Pilulæ Ferri Compositæ_, of our Pharmacopœia afford a very striking example of this peculiar change of consistence, which the mutual reaction of the ingredients produces by simple triture. The _Pilulæ Aloes Compositæ_ offer another instance; for the extract of gentian, upon being triturated with aloes, produces a very soft mass, so that the addition of a syrup, as directed by the Pharmacopœia, is quite unnecessary. See _Form: 12_.