Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/492

474 R E S R E S RESHD. See RASHT. RESIN A, a town of Italy, 6 miles south-east of Naples and practically a southern continuation of Portici, is well known as the usual starting place for tourists on their way up Vesuvius, and as the nearest town to the buried city of Herculaneum. It had 13,626 inhabitants in 1881 (commune 15,593). RESINS. A resin is a secretion formed in special resin canals or passages of plants, from many of which, such as, for example, coniferous trees, it exudes in soft tears hardening into solid masses in the air. Otherwise it may be obtained by making incisions in the bark or wood of the secreting plant. Resin can also be extracted from almost all plants by treatment of the tissue with alcohol, and it is formed by the oxidation of essential oils, many authorities being of opinion that all true resins, which are in chemical composition oxidized hydrocarbons, result primarily from the action of oxygen on essential oils. Resinous substances are further produced by the dry distillation of numerous organic compounds and by the drying of fatty drying oils. Certain resins are obtained in a fossilized condition, amber being the most notable instance of this class, and African copal and the kaurie gum of New Zealand are also procured in a semi-fossil condi- tion. The resins which are obtained as natural exudations are in general compound bodies containing more than one simple resin and varying proportions of essential oil. These compounds when soft are known as oleo-resins, and when imperfectly fluid they are called balsams. Other resinous products are in their natural condition mixed with gum or mucilaginous substances and known as gum-resins. Vary- ing in constitution as these bodies do, they also differ widely in physical properties ; but the general conception of a resin is a noncrystallinQ body, insoluble in water, mostly soluble in alcohol, essential oils, ether, and hot fatty oils, combining with alkalies to form resin soap, soften- ing and melting under the influence of heat, not capable of sublimation, and burning with a bright but smoky flame. A typical resin is a transparent or translucent mass, with a vitreous fracture and a faintly yellow or brown colour, inodorous or having only a slight turpentine odour and taste. Many compound resins, however, from their admixture with essential oils, are possessed of distinct and characteristic odours. A series of gradations among resins may be traced from the hard glassy transparent copals through soft elemis and oleo-resins, semi-fluid balsams and fluid wood oils, to the most limpid essential oils. The hard transparent resins are principally used for varnishes and cement, while the softer odoriferous oleo-resins and gum-resins containing essential oils are more largely used for pharmaceutical purposes and incense. No systematic classification of resins has yet been attempted, and there is much uncertainty as to the botanical source of some well-known commercial varieties, while the chemical con- stitution and relations of many still require elucidation. The following list embraces the principal resins of commerce, and particulars regarding the more important of these will be found under their respective headings, also ROSIN, GUM, and BALSAM. I. Copallinc or Varnish Rosins : African Copal or Gum Aniim (see COPAL, vol. vi. p. 342) ; Mexican Copal, from Hymenca sp. ; Brazilian Copal, from Hymenea s and Trachylubium Afarlianitut ; Piney Resiu, or White Dammar, Valeria indica and V. acuminata ; Sal Dammar, Shorca robusta and other species ; Dammar of Ilopca robusta ; Black Dammar, from Canariitm strictum ; Mastic, P-istacia Lentiscus (vol. xv. p. 621) ; Lac (vol. xiv. p. 181) ; East Indian Dammar (see DAMMAR, vol. vi. p. 795) ; Kaurie or Coudie Resin, Dammara australis (see TURPENTINE) ; Sandarach, from Callitris quadrivalvis (see SANDARACH) ; Dragon's Blood (vol. vii. p. 389). II. Soft or Oleo-Eesins : Manila Elemi, from Canarium com- mune (see ELEMI, vol. viii. p. 122) ; Mexican Elemi, Amijris demi- fera; Brazilian Elemi, Idea Icicariba and other sp. ; Tacamahac (American), Elaplirium tomentosum ; Tacamahac (East Indian), Calophyllum Inophyllum ; Wood Oil, Diptcrocarpus turbinatus ; Chian Turpentine, Pistacia Terebinthus ; Turpentine, Common Frankincense, and Thus from various Coniform (see FRANKINCENSE, TURPENTINE, and ROSIN) ; Balsam of Canada, Abies canadcnsis (see BALSAM). III. Fragrant Olco-Resins and Gum-Resins : Myrrh, Balsamo- dcndron Myrrha (vol. xvii. p. 121) ; Bdellium or Googul, Balsamo- dendron Roxburghii ; Balsam of Gilead or Mecca Balsam, Balsamo- dcndron Berryi ; Olibanum or Frankincense, Bosiocllia Carteri, &c. (see FRANKINCENSE, vol. ix. p. 709) ; Benzoin, Styrax Benzoin and Balsamodendron Miikul (vol. iii. p. 581) ; Solid Styrax, Styrax officinalis (see STORAX) ; Liquid Storax, Liquidambar orientalis (see STORAX) ; Balsam of Peru, Myrospermum peruiferum (see BALSAM) ; Balsam of Tolu, Myrospermum toluiferum ; Labdanum or Ladanum, Cistus creticus, var. labdaniferus. IV. Fetid Gum Resins : Ammoniacum, Dorema ammoniacum (vol. i. p. 742) ; Asaftetida, Ferula Narthex and F. Scorodosma (vol. ii. p. 675) ; Galbanum, Ferula galbaniflua and F. rubricaulis (vol. x. p. 22) ; Opoponax, Opoponax Chironium ; Sagapenum, Ferula sp. ; Sarcocol. V. Medicinal Resins : Gamboge, Garcinia sp. (vol. x. p. 60) ; Guaiacum, Guaiacum ojjkinale (vol. xi. p. 230) ; Euphorbium, Euphorbia resinifera ; Balsam of Copaiba, Copaifera officinalis (see BALSAM). VI. Extract Resins form a class of products principally important from a medicinal point of view. They embrace Scammony from Convolvulus Scammonia, Jalap Resin from Ipomca Jalapa, Podo- phyllum Resiu from Podophyllum peltatum, Churrus from Indian Hemp (Cannabis sativa), Cubeb Resiu from Cubeba officinalis ; and many other medicinal products owe their virtues to resinous bodies present in them. RESPIRATION nnHE continued existence of an amceba in a pool of water, JL or of a white blood-cell in the liquor sanguinis, de- pends upon a continual interchange of substances between the organism and the surrounding medium. The substances in question pass from the medium into the organism in a certain chemical form ; they pass from the organism into the surrounding medium with their chemical form modi- fied. Regarding merely the initial and final stages of this reconstitution of chemical form, we may speak of it as being of the nature of an oxidation. This view does not profess to be comprehensive ; nevertheless, it is true that the metabolic and anabolic processes of cells, taken as a whole, resemble combustion at least to this extent that oxygen and oxidizable carbon take part in them, and that carbon dioxide results from them. Partly as a matter of tradition, and partly as a matter of convenience, physio- logists have described the introduction of oxygen into the organism and the emission of carbon dioxide from it as the complemental portions of one process of resjriratimt. Although such a combined consideration is not strictly philosophical, inasmuch as it leaves out of view the intro- duction of the carbon into the organism, yet it is extremely convenient because the two processes referred to do, in all classes of the animal kingdom from the highest to the lowest, involve the same organs and tissues in their per- formance. Respiration may therefore be denned as the aggregate of those processes which are concerned in the introduction of oxygen into the system and the escape of carbon dioxide from it. Respiration in such an organism as an amoeba is ex- tremely simple. The medium surrounding it contains a practically unlimited supply of oxygen, and is so vast that the carbon dioxide put out into the medium is quickly removed from the neighbourhood of the organism. The