This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Camphor is a concrete substance obtained from Camphora officinarum, an evergreen tree, of considerable size, growing in China and Japan, and other neighbouring countries, and occasionally kept in conservatories in temperate latitudes. The whole plant is impregnated with the camphor, which is separated either by sublimation, or by boiling, and, in the latter case, is sublimed before being sent into market. It comes to us either from the ports of China, or indirectly from Japan through Dutch commerce. As imported, it is not sufficiently pure for use, and is, therefore, submitted to another sublimation, along with a small proportion of quicklime. Thus prepared, it is in large circular cakes, an inch or two in thickness, slightly convex on one side and concave on the other, and perforated in the centre.
As kept in the shops, camphor is usually in fragments of the cakes above mentioned, usually somewhat whitish on the surface, but beautifully clear and translucent within. It has a strong, fragrant, characteristic odour, and a warm, pungent, somewhat bitter taste, which leaves a sense of coolness in the mouth, especially perceptible when the air passes over the tongue during inhalation. It is somewhat unctuous to the touch, and very brittle, yet of difficult pulverization, in consequence of a certain tenacity in its constituent granules, which causes them to flatten under the pestle, without breaking into powder. It may, however, be readily reduced to powder, by first adding a little alcohol, by grating and sifting, or by precipitation by water from its alcoholic solution. Camphor is lighter than water, and, when thrown upon it in small fragments, floats on the surface, and performs various gyratory movements, probably in consequence of the repulsion of its vapour. It is highly volatile, and if exposed to the air will in time wholly disappear. At a temperature somewhat above that of boiling water, it melts, at a higher temperature boils, and at a still higher takes fire, barbing with a brilliant flame, but much smoke, and leaving no residue. In close vessels it may be sublimed unchanged. It is very slightly soluble in water. which, by simple agitation with it, takes up one-thousandth of its weight, and acquires the smell and taste of the camphor. By the Intervention of an agent which enables it to be very minutely divided, as magnesia or its carbonate, it may be dissolved in water in much larger proportion. It is very soluble in alcohol, extremely so in chloroform, and to a considerable extent also in ether, the volatile and fixed oils, strong acetic acid, and the diluted mineral acids; even carbonic acid water dissolving it more largely than water itself. When rubbed with resinous substances, it often loses a part of its odour, becomes softened, and is thus rendered more readily suspensible in water.
Camphor consists of carbon, hydrogen, and oxygen, which are thought to be combined in the form of oxide of camphene, a compound radical consisting of 10 equivalents of oxygen and 8 of hydrogen, and supposed to be identical with pure oil of turpentine.
Another variety of camphor, denominated Borneo, or Sumatra, or Dryobalanops camphor, is obtained from the interstices of the wood of Dryobalanops Camphora, a large forest tree of Sumatra and Borneo. It is never, however, imported for use into America or Europe.
Opinions the most opposite, and facts apparently the most contradictory, have been published in relation to the mode of operation and effects of camphor. Some consider it essentially sedative in its action, whether on the circulatory or nervous system; while others with equal positiveness determine that it is stimulant; and others again think that it may be the one or the other; and facts not to be denied are adduced in support of each opinion. In the present state of our experimental knowledge on the subject, it is impossible to decide with certainty between these conflicting views and statements. More numerous observations, made under every variety of circumstances, and without influence from preconceived opinions, are necessary before any view of its mode of operation can be received as demonstrated. Nevertheless, it may be possible to find some clue through the labyrinth of seeming contradictions; and, after giving a succinct account of the effects produced by camphor, as deduced from the great multitude of published facts, and from ray own personal observation, I shall endeavour to explain them, as far as practicable, in accordance with the general principles maintained in this work.
In the first place, when applied locally, and confined so as to prevent evaporation, camphor produces heat, more or less red-ness, and not unfrequently pain. These effects are not very obvious upon the skin protected by the cuticle; but, when the medicine is applied in concentrated solution, they will, I think, be found to take place in some degree. In blistered and ulcerated surfaces, and in the mouth, they are incontestable. MM. Trousseau and Pidoux state, as the result of personal experiment, that pieces of camphor, held in the mouth for half an hour, had, at the end of that time, produced redness, heat, and painful swelling in the part with which they were in contact. (Mat. Med., 4e ed., ii. 235.) The experiments of Orfila on animals prove that the same effect is produced in the gastric mucous membrane. When camphor was given in small fragments, it was found, after the death of the animal, to have caused inflammation, and numerous small points of ulceration. It is well known that, in man, when swallowed in the form of pill, it is apt to occasion uneasiness or pain in the stomach, and, if in considerable quantities, even nausea and vomiting. It would seem, therefore, that camphor is a local stimulant. But how are we to account for the coldness felt in the mouth when it is swallowed, and, as some assert, even in the stomach? Simply by its volatility. In its conversion from the solid state to that of vapour, it necessarily absorbs heat, and produces the sensation of cold; and this is especially observed when the air is drawn through the mouth, thus favouring the evaporation. There can be no doubt that the same change goes on to some extent in the stomach, under the higher temperature to which the camphor is there exposed, and a necessary result there also is the production of more or less coolness. But excitement of the part is probably not the only effect of camphor. It is scarcely possible that the medicine should have been adhered to, as a local anodyne in rheumatism and other painful diseases, so universally, so pertinaciously, and through so long a series of years, if it really possessed no power of this kind. But nothing is more common, in our experience of the operation of medicines, than the succession of a stimulant and sedative effect. Chloroform powerfully irritates a surface for a time, and afterwards as powerfully reduces its sensibility to painful impressions. Camphor operates in the same way; but, whether its sedative effect on the nervous extremities is direct, or consequent upon a previous stimulant effect upon them, there are no facts which enable us to determine. The question may perhaps be, in some degree, analogically settled, if we can determine how the medicine acts upon the nervous centres; for it is probable, though by no means certain, that it acts upon the same principle in both positions.