Origin

This is the product of Digitalis purpurea, a beautiful herbaceous, biennial or perennial plant, indigenous in Europe, and cultivated in this country as an ornament of gardens, and to a considerable extent also for use. Both the leaves and seeds possess medicinal virtues, the latter even in greater proportion than the former; but the leaves only are officinal, being preferred on account of the much greater quantity produced. They should be collected in the second year of the plant, about the period of inflorescence; and only the full grown and fresh should be chosen. Being injured by an elevated temperature, and by exposure to the air and light, they should be carefully dried by a moderate heat, and kept in well-closed tin canisters, or, if powdered, in glass-stoppered bottles from which the light is excluded. it has been recommended to reject the footstalk and midrib, when they are dried, as these parts are less efficacious than the expanded portion of the leaf; but this caution is often neglected. The leaves should also be dried and preserved separately, and not compressed in the form of those oblong cakes, which are often kept in our shops; for, though the medicine may be of good quality as existing in the cakes, it is liable to be deteriorated, either by the heat employed in drying them, or by the decomposition consequent on the leaves being pressed while moist.

Properties

The leaves, which are attached to the stem by short winged footstalks, are ovate, about eight inches long by three in breadth, pointed, obtusely serrated on their edges, with wrinkled, velvety surfaces, the upper of which has a fine deep-green colour, the under is more downy, and paler. They are inodorous when fresh, but acquire upon drying a faint narcotic smell. Their taste is bitter and nauseating, and their colour when dried a dull green. in powder they are of a fine deep green. As found in the shops, they are extremely variable in strength, partly from original deficiency, and partly from changes after collection; yet there are few medicines in which uniformity of strength is more desirable; as, being usually administered in small doses at first, to be gradually increased till their effects are experienced, which is sometimes not for several days, much valuable time is lost in the preliminary trial, if they should turn out to be feeble or inert. The best test which the physician can apply is that of the senses. He should take care that only the proper substance of the leaf is used, that it has the green colour without brownish stains, and that the characteristic bitter and nauseating taste should be very obvious. The medicine imparts its virtues readily to water and alcohol. These virtues reside exclusively in a peculiar principle called digitalin, which, as it is separated for use, and employed to a considerable extent, will be described among the preparations. According to M. Homolle, who has investigated the chemistry of digitalis with great care and success, though digitalin (or as he calls it digitaline) represents all the remedial virtues of digitalis, there is another constituent called digitaleie acid, belonging to the fatty acids, which is acrid and nauseous, and to which the leaves owe mainly their nauseating properties. As this principle is insoluble in water, though dissolved by alcohol, it follows that the infusion or aqueous extract of digitalis should be preferred to the tincture, or any other preparation made through the solvent powers of alcohol or ether. (Arch. Gén., Juillet, 1861, p. 25.) By destructive distillation, the leaves yield a poisonous empyreumatic oil, which contains no digitalin.

1. Effects On The System

Digitalis is locally excitant, but powerfully sedative to the nervous and circulatory systems, and stimulating to the function of the kidneys. When the powder is applied to the skin denuded of the cuticle, or to a mucous surface, it causes painful irritation, and, if continued, inflammation, sometimes followed by ulcers. Of course, this locally irritant property is exercised upon the stomach, when the medicine is swallowed in sufficient quantity, and must be taken into account in explaining certain effects of digitalis, which might otherwise be very wrongly interpreted.

Given in the regular medicinal doses, repeated at the proper intervals, and gradually increased if necessary, digitalis is often, as I know from frequent observation, without any apparent effect upon the system for several days. in other instances, its peculiar influence is felt in a few hours, and sometimes very speedily. These differences depend partly on difference of strength in the medicine, and partly also on the extremely variable susceptibility to its influence in different individuals. Nor is the character of the effect which is first produced always the same. in some instances its local operation is first evident, in others its action on the kidneys, and in others again its sedative influence on the heart, or the nervous centres. As a general rule, the local effect of the medicine, in the doses referred to, is scarcely felt; at least this is certainly true in the great majority of cases. Most frequently it is either the diuretic action, or that upon the circulation, which is first experienced. Of the former of these I shall treat under the diuretics, and will merely further observe here, that it is often very powerful, and of inestimable service in the treatment of dropsical diseases. it is with the sedative operation of digitalis that we are here concerned. This is usually first evinced in the diminished frequency of the pulse, and afterwards in the production of nervous symptoms.

On the Circulation. The great majority of observers agree in the statement that the first effect of digitalis, in medicinal doses, upon the pulse, is to diminish its frequency. This has been noticed, not only in relation to man, but also in the inferior animals. in some carefully conducted experiments upon the horse, by MM. Bouley and Reynal, of the veterinary school of Alfort, the result in every case, when the medicine was given in a therapeutic dose, was to reduce the frequency of the pulse and the number of respirations, the former effect generally commencing in eight or ten hours, and continuing for a day or more. (MM. Homolle and Quevenne, Arch, de Physiol, Jan. 1854, p. 223.) in man, when the medicine acts, the greatest amount of reduction usually occurs in from four to six hours after its administration. The degree to which the reduction sometimes takes place is very great. From the natural standard, the pulse not unfrequently falls to fifty in the minute, and instances have been observed in which it has sunk to thirty, and even lower. I have often noticed that, with the diminution in the frequency of the pulse, there is an increase in its volume, but not, as some have stated, in its force. On the contrary, the resistance under the fingers is generally if not invariably diminished, in the normal state of the system; and, if the influence of the medicine is increased, it may become extremely feeble.