[638] Transac. of the New Zealand Inst., vol. ii., 1869; Brit. and For. Med. Chir. Review, July 1871, p. 230.
§ 629. Ants.—The various species of ants possess at the tail special glands which secrete formic acid. Certain exotic species of ants are provided with a sting, but the common ant of this country has no special piercing apparatus. The insect bites, and then squirts the irritating secretion into the wound, causing local symptoms of swelling and inflammation.
§ 630. Wasps, &c.—Wasps, bees, and hornets all possess a poison-bag and sting. The fluid secreted is as clear as water, and of an acid reaction; it certainly contains formic acid, with some other poisonous constituent. An erysipelatous inflammation generally arises round the sting, and in those cases in which persons have been attacked by a swarm of bees, signs of general poisoning, such as vomiting, fainting, delirium, and stupor, have been noticed. Death has occasionally resulted.
§ 631. Cantharides.—Commercial cantharides is either the dried entire, or the dried and powdered blister-beetle, or Spanish fly (Cantharis vesicatoria). The most common appearance is that of a greyish-brown powder, containing shining green particles, from which cantharidin is readily extracted by exhausting with chloroform, driving off the chloroform by distillation or evaporation, and subsequently treating the extract with bisulphide of carbon, which dissolves the fatty matters only. Finally, the cantharidin may be recrystallised from chloroform, the yield being ·380 to ·570 per cent. Ferrer found in the wings and their cases, ·082 per cent.; in the head and antennæ, ·088; in the legs, ·091; in the thorax and abdomen, ·240; in the whole insect, ·278 per cent. Wolff found in the Lytta aspera, ·815 per cent.; Ferrer in Mylabris cichorei, ·1 per cent.; in M. punctum, ·193; and in M. pustulata, ·33 per cent. of cantharidin.
§ 632. Cantharidin (C10H12O4) has two crystalline forms—(1) Right-angled four-sided columns with four surfaces, each surface being beset with needles; and (2) flat tables. It is the anhydride of a ketone acid (cantharidic acid), C8H13O2-CO-COOH. It is soluble in alkaline liquids, and can be recovered from them by acidifying and shaking up with ether, chloroform, or benzene; it is almost completely insoluble in water. 100 parts of alcohol (99 per cent.) dissolve at 18° 0·125 part; 100 of bisulphide of carbon, at the same temperature, 0·06 part; ether, ·11 part; chloroform, 1·2 part; and benzene, ·2 part. Cantharidin can be completely sublimed, if placed in the subliming cell (described at [p. 258]), floating on mercury; a scanty sublimate of crystals may be obtained at so low a temperature as 82·5°; at 85°, and above, the sublimation is rapid. If the cantharidin is suddenly heated, it melts; but this is not the case if the temperature is raised gradually. The tube melting-point is as high as 218°. Potassic chromate with sulphuric acid decomposes cantharidin with the production of the green oxide of chromium. An alkaline solution of permanganate, iodic acid, and sodium amalgam, are all without influence on an alcoholic solution of cantharidin. With bases, cantharidin forms crystallisable salts, and, speaking generally, if the base is soluble in water, the “cantharidate” is also soluble; the lime and magnesic salts dissolve readily. From the soda or potash salt, mineral acid will precipitate crystals of cantharidin; on heating with pentasulphide of phosphorus, o-xylol is produced.
§ 633. Pharmaceutical Preparations of Cantharides.—The P.B. preparations of cantharides are—Acetum cantharides, or vinegar of cantharides, containing about ·04 per cent. of cantharidin.
Tincture of cantharides, containing about ·005 per cent. of cantharidin.
A solution of cantharides for blistering purposes, Liquor epispasticus, a strong solution of the active principle in ether and acetic acid, containing about ·16 per cent. of cantharidin.