458 
ON THE ANATOMY OE DRUGS. 
hitherto received species greatly reduced; indeed the infinite variety of form, 
assumed by the single species of which common “ Blue Mould ” is an example, 
affecting not only vegetable substances, but even living animals up to man him¬ 
self, is one of the most wonderful instances of variation within specific limits 
with which we are acquainted. 
Possibly the Lichens are of even less importance medicinally than the Fungi^ 
and the family is represented in the Pharmacopoeia by but one species, Cetraria 
Islandica. Whilst closely related to the Fungi in many physiological points. 
Lichens possess several peculiarities of structure which cannot be passed over, 
and the officinal Cetraria is a fair example for description. The plant is familiar 
enough ; it consists of a dry, dull-coloured, leafy thallus or frond growing erect, 
the margin broken into lobed segments, and edged by a tooth-shaped fringe. 
A section of the thin portion of the frond shows under the microscope a tolerably 
distinct separation of the systems of cells. On either surface four or five rows 
of thick-walled cells form a sort of epidermis, and this is again lined by a layer 
of long, nearly straight, cylindrical cells, closely compacted. The central portion 
consists of light spongy tissue, made up of loosely felted cylindrical cells with 
vacant air-spaces. Lying on the inner surface of the inner layer, between it and 
the spongy central portion, may be found minute greenish spheres {gonidia)^ 
which are the means of vegetative reproduction, answering to the buds of higher 
plants. At the margin of the larger lobes of the frond the true fructification 
appears, though it is not so commonly seen in commercial specimens as might be 
expected. This consists of brown or reddish shield-shaped bodies with raised 
edges (apothecia)^ which contain the iJieccB or spore-cases. 
Passing from the Lichens to the Alga, we again find a few plants of sufficient 
interest to merit attention, though no species now recognized as officinal. The 
most familiar to the pharmaceutist is the so-called Carrageen, or Irish Moss 
(Chondrus crispus), but even this can scarcely be considered as a medicine, 
but rather, in company with some other of our native marine Alga, as a dietetic 
substance. Fucus vesiculosiis (Bladder-wrack) has recently been vaunted in the 
treatment of obesity, but its employment in this country has been limited. The 
structure of the stems and fronds of the larger marine Alga is more or less con¬ 
formable to one general type. They are entirely cellular, and can scarcely be 
said to exhibit any well-defined separation into the systems we recognize in more 
highly organized plants. The only approach to such a distinction is in the 
difference between the central and external portions, but they never present 
anything like a true bark, or even a separable epidermis. A longitudinal section 
shows the superficial portions to be composed of small, compact, thick-waUed 
cells, whilst the central tissues are formed of cells of much larger size, either 
oval or angular in form, or of a long cylindrical shape, somewhat interwoven. In 
some species a moderately well-defined line marks the boundary between the 
two forms of cells, but in others the transition is very gradual. Through the 
whole group we find only the changes rung on the various forms of the simple 
cell. We venture to object to Dr. Pereira’s figure of the structure of the frond 
of Chondrus (especially that of the transverse section), as it represents, if cor¬ 
rectly drawn, a very exceptional instance of differentiation in the tissues. Dr. 
Berg’s plate gives a much more accurate reading of its microscopic appearance. 
A very important medical application has recently been made for the stems 
of some of the larger Alga, depending for its utility on the peculiar structure of 
■'diheir tissues. The thick-walled character of the cells, and the mode in which they 
are combined, produces a strong cartilaginous texture, which, when deprived of 
water by careful drying, shrinks into a relatively very small compass, and be¬ 
comes tough and hard like gutta-percha. On access of moisture gradual ex¬ 
pansion to the original size and form takes place. Hence the exsiccated stems 
of Laminaria (Sea-tangle) are now used in the preparation of bougies and tents 
