Secretion—All the green parts of the plant are traversed by a system of vessels, which when wounded, especially during the period of flowering, instantly exude a white milky juice. The stem, at first solid and fleshy but subsequently hollow, owes its rigidity to a circle of about 30 fibro-vascular bundles, each of which includes a cylinder of cambium. At the boundary between this tissue and the primary cortical parenchyme, is situated the system of milk-vessels, exhibiting on transverse section a single or double circle of thin-walled tubes, the cavities of which contain dark brown masses of coagulated juice. In longitudinal section, they appear branched and transversely bound together, as in the milk-vessels of taraxacum. The larger of these tubes, 35 mkm. in diameter, correspond pretty regularly in position with the vascular bundles. Each of the latter is also separated from the pith by a band or arch of cambium, in the circumference of which isolated smaller milk-vessels occur.
The system of milk-vessels[1457] is therefore double, belonging to the pith on the one side, and to the bark on the other, the two being separated by juiceless wood. The milk vessels of the bark are covered by only 2 to 6 rows of parenchyme-cells of the middle bark, rapidly decreasing in size from within outwards, and these are protected by a not very thick-walled epidermis. Hence it is easy to understand how the slightest puncture or incision may reach the very richest milk-cells.
The drops of milky juice, when exposed to the air, quickly harden to small yellowish-brown masses, whitish within.
Collection and Description—Lactucarium has been especially collected since about the year 1845, in the neighbourhood of the small town of Zell on the Mosel between Coblenz and Trèves in Rhenish Prussia. The introduction of this industry is due to Mr. Goeris, apothecary of that place, to whom we are indebted for the following information, and for some further particulars, to Mr. Meurer of Zell.
The plant is grown in gardens, where it produces a stem only in its second year. In May just before it flowers, its stem is cut off at about a foot below the top, after which a transverse slice is taken off daily until September. The juice, which is pure white but readily becomes brown on the surface, is collected from the wounded top by the finger, and transferred to hemispherical earthen cups, in which it quickly hardens so that it can be turned out. It is then dried in the sunshine until it can be cut into four pieces, when the drying is completed by exposure to the air for some weeks on frames.
At Zell, 300 to 400 kilogrammes (661 to 882 lb.) of lactucarium are annually produced; the whole district furnishes at best but 20 quintals annually. The price the drug fetches on the spot varies from 4 to 10 thalers per kilogramme (about 6s. to 14s. per lb.) In the Eifel district, where lactucarium was formerly collected, none is now produced.
As found in trade, German lactucarium consists of angular pieces formed as already described, but rendered more or less shrunken and irregular by loss of moisture and by fracture. Externally they are of a dull reddish-brown, internally opaque and wax-like, and when recent, of a creamy white. By exposure to the air, this white becomes yellow and then brown. Lactucarium has a strong unpleasant odour, suggestive of opium, and a very bitter taste.
The lactucarium produced by Aubergier of Clermont-Ferrand is of excellent quality, but does not appear to differ from that obtained on the Mosel, except that it is in circular cakes about 1½ inches in diameter, instead of in angular lumps.
Scotch lactucarium, which was formerly the only sort found in the market, is still (1872) met with. Mr. Fairgrieve, who produces it in the neighbourhood of Edinburgh, collects the juice into little tin vessels, in which it quickly thickens; it is then turned out and dried with a gentle heat, the drug being broken up as the process of drying goes on. It is thus obtained in irregular earthy-looking lumps of a deep brown hue, of which the larger may be about an inch in length. In smell, it exactly resembles the drug collected on the Continent.[1458]
We have also before us Austrian lactucarium, prepared at Waidhofen on the Thaya, where about 35 kilogrammes are annually produced. It is in fine tears of vigorous smell.