76

ELEMENTS OF MATEKIA MEDICA.

cannot be referred to the latter. We therefore ascribe them to theirspecific impressions on the nerves of the part to which they areapplied.

The effects of the substances composing this group are very quicklyproduced, and soon disappear. Consequently these remedies are adaptedto urgent and acute cases, when the danger is imminent, and an immediateeffect desired: for the same reason they require to be frequentlyrepeated in order to keep up their effects. From their exciting opera-tion they are indicated in cases of debility and sinking of the vitalpowers. Thus they are employed in syncope, low fevers, cholera, &c.On account oi their specific influence over the nervous system they areadministered in various spasmodic or convulsive diseases, especially inhysteria, and also in epilepsy and chorea.

f The sixth group contains camphor, the roots of serpentary, con-trajerva, and valerian, the oil of cajuputi, &c. It corresponds with thatdivision of volatile excitants called by Vogt, atherio-oleosa; it is a lessperfect group than any of those already mentioned. To a certain extentit agrees in its effects with the last mentioned: thus it specificallystimulates the nervous system, increases the activity of the vascularsystem, and produces diaphoresis. Its effects, however, are much lesspowerful, are not so speedily produced, nor arc they so fleeting. Someof the substances of this group (for example, serpentary and contrajerva)are serviceable in low nervous fevers; others are used in spasmodicdiseases, as valerian in epilepsy.

g. The seventh and last group is the spirituosa of Vogt. It compre-hends those substances already mentioned under the head of cerebro-spinants, as inebriating; namely, alcohol, wine, and ether. Theireffects and uses will be fully described in a subsequent part of thiswork.

Active principles. —Volatile oil and resin are the most common con-stituents of the foregoing groups.

1. Volatile oil {oleum volatile, vel rather eum, seu essentiale). —Volatile oil isfound in both the inorganised and organised kingdoms of nature : it is mostcommon in vegetables. Petroleum and naphtha are examples of volatileoil in the mineral kingdom. Among animal substances castoreum maybe referred to as containing it. It is found in various parts of vegetables—as in the cortical parts of their stems, in cinnamon and cassia; in theirrhizomes, as in ginger and Acorus Calamus; in the root, as in valerianand horse-radish ; in the leaves, as in buchu, Labiatce, and Myrtacem; inbuds, as in the bulbs of garlic and onions; in fruits, as the orange andUmbellifen e; and sometimes, though very rarely, in the seeds, as in thenutmeg. From these different parts it is occasionally obtained by pres-sure, but more commonly by distillation.

The volatile oils may be solid or liquid at ordinary temperatures;when solid they are crystalline. They may be lighter or heavier thanwater; their sp. gr. varying from O'627 to 1 004 ( Gmelin ). They may becoloured or colourless ; if the former, the tint is various in different oils.All the essential oils have a strong odour, and a hot acrid taste. Theyare easily volatilised by heat; are combustible, in consequence of thelarge quantity of carbon and hydrogen which they contain; and aredecomposed by chlorine, iodine, bromine, and the acids. Some of them(as the oil of turpentine) combine with hydrochloric acid. They are very