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ELEMENTS OF MATERIA MEDICA.

benefit. Swallowed to the extent of 24 grains, it gave rise to i sweetishtaste and a slight feeling of internal heat, hut no other symptom.— {Diet ,des Drogues .)

5. Extractive. —Some of the vegetable tonics are said to owe theirbitterness and medicinal activity to a principle to which the terms jmateria hermaphrodita, materia saponacea, and extractive mat,ter, have >been applied. It is described as being of a brown colour, soluble in |water and alcohol, insoluble in ether, and becoming insoluble in water }by long-continued boiling and by exposure to light and aii. That a |substance, or mixture of substances, possessed of these properties, may *be obtained from various plants, cannot be doubted, but it is no; probable jthat chemists have yet succeeded in obtaining a proximate principle to 3which the term extractive can with propriety apply. What has hitherto 'been procured is a mixture or compound of several principles, such as 'vegetable acids and their combinations with potash and lime, colouringmatter, sugar, gum (rendered soluble in alcohol by its combination withother substances), vegetable bases, &c.

Class 4.— Emollients. —The substances called emollients diminishthe tonicity or insensible contractility of the living tissues to which theyare applied, and thereby occasion local relaxation and weakness. They ■have an operation diametrically opposite to tonics,—especially to those ;which are astringent. They relax, soften, and swell the tissues, and ren- jder them more flexible. Applied to inflamed parts they dimmish heat,tension, and pain, and oftentimes assist in producing the resolution of thedisease ; and when the inflammation is too violent, or too far advanced,for this to be effected, they are useful by promoting suppuration. Theyhave a relaxing effect on the muscular fibre, and are, therefore, em-ployed to relieve spasm. These effects have been referred by someto a physical, by others to a vital agency. During life the particles ofthe body are kept in approximation by tw r o forces—attraction and thevital principle; and as emollients render the parts to which they areapplied soft and flexible, that is, produce relaxation, it becomes a (pies- :tion whether they operate by overcoming the cohesion of the molecules, Ior by modifying the vital properties. Most writers have regarded them jas mechanical agents, and explain their influence just as they would the |action of warm water, or oil, on inorganic substances—leather, for exam-ple. But we should always be cautious in applying physical explana-tions to vital phenomena ; and in the present instance this is particularlynecessary. That emollients act on physical principles on iuorganisedparts of the body (the cuticle, for example) cannot be doubted, though wocannot admit tills explanation in reference to living parts. Cold waterdiminishes the cohesion of dead parts, and renders softer and more flexi-ble, but it has not the same effect on living tissues. Moreov er, Dr. A.Crawford (op. cit.) ascertained that some medicinal agents diminish thecohesion of dead animal tissues, and have an opposite effect on the livingtissues.

The constitutional effects of emollients are for the most pait those ofnutrients, not of medicines ; though the continued use of some is said todiminish the tone or vigour of the system generally—an effect ascribedby Barbier ( Traite Elementaire de Matiere Medicate), to their absorptionand local action on all the fibres of the body. This statement, however,is unsupported by fact in the case of gum, starch, sugar, gelatine, albu-