An agent so powerful for good is necessarily capable of doing mischief, if abused or improperly used.

1. When, from idiosyncrasy, mercury has been found to act injuriously, its use in the same individual should be subsequently resorted to with great caution, and only under urgent circumstances. Of course, the peculiarity of excessive susceptibility to its sialagogue action is no positive contraindication; as its evil effects can be avoided by a degree of caution, in the use of the medicine, proportionate to the susceptibility; but it should serve as an inducement to the utmost watchfulness, and should prevent a resort to the medicine on all trivial occasions.

2. The suppurative and gangrenous states of inflammation, and the gangrenous condition generally, are incompatible with the use of mercury, which, by depreciating still further the character of the blood, and favouring the disintegration of the tissues, would have a tendency to aggravate the affection. A slight degree of suppuration, while the element of excitation still predominates in the inflamed part, should not be allowed to prevent its use, when it is important to limit the inflammation; but it should always be omitted, when either suppuration or gangrene has become fully established. The occurrence of hectic symptoms should generally be received as a signal for suspending its use. To the condition denominated metastatic abscess, suppurative phlebitis, and purulent infection of the blood, it is altogether unsuitable.

3. Fatty degeneration, or a tendency towards it, is another condition in which mercury can do only harm. in this, the powers of life in the system at large, or in the part, are enfeebled, and mercury would enfeeble them still further. Besides, it would seem, from the analysis of mercurialized blood by Dr. Wright, that it abounds in fatty matter, showing a strong tendency in mercurialism to favour the oleaginous conversion of the tissues. Hence, the medicine has been found injurious in chronic Bright's disease, and should never be used when any considerable amount of oil is discoverable in the urine in that affection, or there may be good reason, from any other cause, to believe that it is connected with fatty degeneration of the kidneys. The same remark is applicable to cases in which there may be any suspicion of similar degeneration of the brain or heart.

4. An anemic or otherwise impoverished condition of the blood, though it should not be considered as forbidding the use of mercury, when strongly indicated by other coexisting conditions, should be allowed to weigh against it, in doubtful cases; and, when it may be deemed proper or necessary to administer mercury, in such a state of system, care should be taken to guard the blood, as far as circumstances will permit, against further deterioration.

5. in the scorbutic state of the blood, and that which attends and characterizes a malignant condition of system, in which coagulability is imperfect or wanting, the fibrin is defective or depraved, and the red corpuscles more or less disintegrated, mercurialization is altogether contraindicated; and, when this condition supervenes upon one in which the medicine is employed, it should immediately be suspended, until the blood has been restored to its proper condition.

6. Analogous to the above state of the system are those in which there is a disposition to phagedenic or gangrenous ulceration, or to passive hemorrhages. Even in syphilis, mercury should be withheld, or omitted, when such a tendency becomes obvious.

7. Diseases of the spleen are usually ranked among the contraindi-cating conditions; and, certainly, in that depraved state of the blood which is so apt to attend them, mercury would seem to be forbidden. Experience, too, has shown that chronic engorgements of that viscus yield less readily to mercury than similar affections of the liver; but, in simple splenitis, whether acute or chronic, if the system is not anemic, or the blood depraved, I should have no hesitation in resorting to a careful course of mercury, should the affection resist other antiphlogistic treatment.

8. The existence of a tuberculous or scrofulous diathesis is now generally admitted to contraindicate the use of mercury. So far as the mere inflammation is concerned which attends this diathesis, the medicine has often been found to exercise a curative influence; but it is at the expense of the general system, and at the risk of increasing the disposition to tuberculous deposit. Formerly it was very customary, in this country, to treat phthisis with mercury; but the general experience was that the progress of the disease was hastened; and this application of the medicine has been universally abandoned. in all the scrofulous affections, there is a disposition to an anemic or otherwise impaired state of the blood, which is now believed to favour the formation of tubercle. Mercury has been shown experimentally to have a similar effect on the circulating fluid. Reason, therefore, as well as experience, would forbid it in affections of this kind. There may possibly supervene, upon a scrofulous or tuberculous constitution, some affection to which mercury is peculiarly appropriate, iritis or hepatitis for example, and which might do more injury to the patient than mercurialization would be likely to inflict. Under such circumstances, the physician would be justified in resorting to a very careful use of the remedy, precisely as, in a similar condition, he might be compelled to resort to direct depletion, which is perhaps quite as injurious in relation to the constitutional affection. But mercury should never be used with a direct view to prevent or cure tubercles themselves, and with extreme caution, if ever, to obviate the inflammation which arises directly from them.

9. Finally, carcinoma, melanosis, cirrhosis, fibroid degeneration, and similar abnormal conditions, as they are wholly incurable by mercury, and themselves tend to a gradual reduction of the vital forces, should be considered as offering contraindications to its use.

But, in reference to most of the above pathological states, the contraindication must be understood to be against the use of mercury, carried so far as to produce its effects on the system, and not against its pure alterative use in disorders of the digestive organs, connected with deranged action of the liver, or its employment as a cathartic. Under these circumstances, its influence is mainly confined to the chylopoietic viscera, and is not exerted upon the system at large, or directly on the blood.