This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Leeches are aquatic worms, and are bred in ponds for medicinal use, chiefly in Germany (near Hanover) and in the south of France (near Marseilles). Two varieties are official - viz. the speckled leech, Hirudo medicinalis, Linne, and the five striped or Australian leech, Hirudo quinquestriata, Schmarda (Phylum Annelida, Class Hirudinea, Order Gnathobdellida); they may be distinguished by the ventral surface, which in the former is of a greenish yellow colour, spotted with black, whilst in the latter it is not spotted.
Although the dorsal surface of the leech is marked with numerous (about 100) annulations, the body is not divided into distinct segments. It tapers towards each extremity, and is provided at each with a sucking-disc by which it can attach itself to any object. The anterior disc, which is smaller than the posterior, contains three jaws radiating from a common centre; each jaw is furnished with a number of minute teeth, and resembles a portion of a circular saw. The animal attaches itself by means of its anterior sucker to the skin, which is thereby slightly raised; the three jaws, by a saw-like movement, produce three slits which unite to form the characteristic triradiate cut, and the leech gorges itself with blood; it then relinquishes its hold, and drops from the skin. The blood which it has drawn is so slowly digested that a single meal will last for several months.
Although the leech is hermaphrodite - that is, both sexes are united in the same individual - it is incapable of self-fertilisation. It reproduces itself by means of eggs, and the young require about five years to arrive at maturity.
The quantity of blood that a leech will draw is not large (from 4 to 8 c.c), but the flow of blood from the cut is often continued for some time; this appears to be due partly at least to a substance, hirudin, which is secreted by the salivary glands of the leech and injected into the cut. The flow of blood can also be maintained by fomentation.
Leeches are used to reduce inflammation by withdrawing blood. Hirudin, which retards the coagulation of blood, has been suggested for use in thrombosis and other conditions in which the blood shows a disposition to clot too readily.
(Spanish Flies, Cantharis)
Cantharides are the dried beetles, Cantharis vesicatoria, Latreille (Lytta vesicatoria, Linne, Phylum Arthropoda, Class Insecta, Order Coleoptera).
Cantharides, or, as they are frequently termed, Spanish flies, are widely distributed over southern Europe; they are gregarious and inhabit chiefly ash trees, privets, elders, etc. They are collected in the very early morning before sunrise (whilst they are unable to use their wings) by shaking them from the trees on to cloths placed beneath; they are killed by exposing them to the fumes of ammonia, acetic acid, or burning sulphur, or by stove heat; they are then dried, preferably by stove heat. When fresh they possess a powerful, disagreeable odour, which diminishes by keeping.
They are collected in southern Russia, Galicia, Roumania, and also to a much smaller extent in Italy and Spain.
Cantharides are about 20 to 25 mm. long, about 7 mm. broad, smooth, and of a shining green or coppery green colour. The wing-cases are long and narrow, and conceal two transparent, brown, membranous wings. Each insect possesses three pairs of legs and one pair of antennae.
The principal constituent of cantharides is a definite crystalline body, cantharidin, which, although almost insoluble in cold water and only sparingly soluble in alcohol, dissolves readily in acetic ether, chloroform, and benzene. With caustic alkalies (potassium or sodium hydroxide) it unites to form soluble salts, and there is evidence to show that in the beetles it exists partly as free cantharidin, partly in the form of salts soluble in water. The soft parts of the insect are the chief seat of cantharidin. Good cantharides contain from 0.5 to 0.8 per cent. or occasionally as much as 1 per cent.
In addition to this substance the beetles contain about 12 per cent. of fixed oil.
Fig. 245. - Spanish blistering beetle, Cantharis vesicatoria. Slightly enlarged. (Maisch).
Moisten 20 gm. of finely powdered cantharides with 3 c.c. of hydrochloric acid, transfer to a Soxhlet apparatus and exhaust with benzene. Distil off the benzene and boil the residual fatty matter for 10 minutes with 100 c.c. of water acidified with hydrochloric acid, using a reflux condenser. Transfer the hot aqueous solution to a capacious separator, and repeat the boiling with four successive portions of 50 c.c. of water, unite the aqueous solutions, and shake out with successive portions of 30, 30, 20, and 20 c.c. of chloroform. Recover the chloroform by distillation from a tared flask, dry the residue at 60°, and wash first with 10 c.c. of a mixture of equal volumes of absolute alcohol and petroleum spirit, and finally with petroleum spirit until the latter leaves no appreciable residue on evaporation. Dry at 60° and weigh.
Cantharides possess rubefacient and vesicant properties; given internally, the drug acts as an irritant poison.
The number of species of Coleoptera known to possess vesicating properties is very large, but only a few are employed for that purpose. The most important of these are Chinese blistering beetles (Chinese cantharides), large quantities of which are regularly imported. They are derived from two species, viz.:
1. Mylabris sidoe, Fabricius (M. phalerata, Pallas). This varies from 12 to 30 mm. in length, and from 5 to 10 mm. in breadth. It is black in colour, but the wing-cases are traversed by three broad, brownish yellow bands. These bands bear black, bristly hairs which, however, are not readily seen in the commercial drug, as most of them have been broken off. The beetles inhabit China, Bombay, Assam, etc.
2. Mylabris cichorii, Fabricius, on the average smaller than the foregoing; it varies from 10 to 15 mm. in length, but is marked with similar yellow bands, which, however, are usually brighter in colour. The chief distinction of this species lies in the yellow downy pubescence with which the yellow bands are covered, the hairs on the black bands being black. It inhabits China and eastern India.
Chinese blistering beetles contain from 1 to 1.2 percent. of cantharidin and form a useful source of this substance.
In addition to these, several other blistering beetles find their way occasionally to London, e.g. M. lunata, Pallas, and M. bifa-sciata, Oliver, from South Africa, Epicauta gorhami, Mars, from Japan, etc.
C. quadrimaculatus (Mexican cantharides) have been imported into Hamburg; they resemble M. cichorii but have only two black bands on the wing-cases.
Admixture with (entire) exhausted beetles can be detected by the deficiency in cantharidin and in fat.
The drug is seldom adulterated, but accidental admixtures are occasionally met with.
Fig. 246. - Chinese blistering beetle, Mylabris sidoe ( = M. phalerata, Pall.). (Maisch.)1
1 Maisch's figure is apparently erroneously named M. cichorii.