Effects of the Cerate. For a short time after the application, no perceptible effect is produced. Soon, however, a slight sense of warmth and perhaps of tingling is experienced, which is probably coincident with a moderate increase of the perspiratory function, whereby the skin becomes moist, and thus facilitates the further action of the irritant. This sensation gradually increases to a burning pain, which is sometimes very severe, sometimes quite tolerable, according to temporary or constitutional differences in susceptibility. if the surface is now examined, it is found much reddened, though not so deeply as by some of the more powerful rubefacients. in a short time, it becomes covered with innumerable vesicles, which gradually enlarge into bullae, until at length the whole or nearly the whole of the epidermis is separated, and a light-yellowish translucent liquid is collected beneath it. The liquid has been found to contain about six per cent. of albumen, with some salt, besides water. Occasionally it coagulates, and the blister appears Oiled with a tremulous jelly, which, however, gradually disappears under dressings.

The blister is now said to have drawn. The period required for the process varies exceedingly under different circumstances. it is shorter in parts covered with a delicate epidermis than in others, consequently on the inner side of the limbs than the outer, and probably on the anterior surface of the body than the posterior. in women the process is more rapid than in men, and in children than either. in an adult man, vesication may usually begin in three or four, and be completed in from eight to twelve hours; but the latter period is often much exceeded, and the former sometimes anticipated. in hairy parts, even though shaven, almost twice as much time is requisite as for a surface destitute of hair.

During the rubefacient stage, there is generally some constitutional excitement, which has already been sufficiently considered in the general observations. But an incident frequently happens, in the course of the vesication, which it is necessary to notice. I allude to strangury. This, as before stated, when cantharides was treated of in reference to its effects on the system, is an almost constant result of its internal use, when pushed sufficiently far. it often occurs from its external application, but by no means so uniformly. There seems, in some persons, to be a strong constitutional liability, so that they are always affected; in others a constitutional exemption, so that they never suffer. The affection is undoubtedly owing to the absorption of the active principle. I have generally noticed that it comes on only after vesication has taken place; as if the intervention of a liquid between the medicine and the absorbing surface, favoured the passage of the cantharidal solution en-dosmotically into the blood-vessels. M. Mialhe states that the more quickly the vesication is produced, the more apt the patient is to escape strangury. {Journ. de Pharm. et de Chim., 3e sér., xlii. 54.) The symptoms of strangury were described in the general account of the operation of the medicine; and I need not repeat them here. They are precisely the same in character, whether produced by its internal or external use. (See vol. II. p. 643.)

When the vesication is complete, and the serum has escaped through spontaneous or artificial openings, the vesicated surface will usually heal kindly, if the loosened epidermis be allowed to remain, so as to protect it from the air. if it be removed, however, the surface is apt to become irritated, and sometimes severe and highly painful inflammation occurs, which occasionally ends in suppuration. The same effect takes place, in consequence of the application of irritant dressings. Under these circumstances, however, instead of producing pus, the surface often throws out coagulable lymph, which forms a protective layer against the influence of the irritant. Occasionally, from the application of severe irritants, too long continued, and sometimes without them, in persons of enfeebled constitution, and diseases attended with depraved blood, ulceration takes place, and even gangrene, which may be dangerous to life. When there is, at the same time with the use of the remedy, a disposition to erysipelas, it sometimes happens that the blistered surface becomes the seat of this affection, which spreads from it on all sides. in some very rare instances, probably in consequence of the absorption of the cantharidin, serious constitutional disturbance arises, marked, besides the moderate febrile symptom before mentioned, with dryness of the mouth and fauces, subsultus tendinum, and even convulsions. Such cases, however, are extremely rare; and I cannot recall more than one instance, in which I thought the condition fairly ascribable to the medicine.

Treatment of the Blisters. The first question is how long the application is to continue ? in general until vesication has completely taken place, or, to use the ordinary mode of expression, until the blister has fully drawn. For the most part, in an adult man, it may continue twelve hours, and upon the scalp from eighteen to twenty-four hours. it is an error to withdraw the cerate too soon. The object is not simply to vesicate. it is to establish a certain amount of inflammation in the part, sufficient for a powerful excitant and revulsive impression. This object is not gained, oris gained but imperfectly, with a premature removal. Circumstances, however, may require a shorter period. Thus, in very sensitive parts, and those of loose texture, the cerate may be removed in six or eight hours, because vesication occurs sooner in these parts than elsewhere; and, if the application continue, extensive inflammation, with edematous effusion, is apt to take place in the loose cellular tissue. This not unfrequently happens when a blister is applied over the eye, or to the scrotum. The supervention of stran gury often also calls for an earlier removal than under ordinary circumstances. in children, the period of application must be much shorter than for adults. in infants under two years, the cerate should be removed in two or three hours; in a child from two to four years, in four or five hours; and these periods may be anticipated, if, on examination, it should appear that vesication had occurred. The danger is peculiarly great, in young children, from too long an application of the remedy, which may occasion mortification of the surface, especially in low cases of exanthematous fever, as scarlatina and malignant small-pox.