Potash has been already considered. Bromine and free Chlorine are very analogous to Iodine in their operation.
Antiarthritics exert an influence on the blood. This is least apparent in the case of Colchicum, which is a somewhat mysterious remedy. But it has been said by some to increase the amount of Urea in the urine; by others, to promote the excretion of Uric acid. (Vide Antiarthritics, and Chap. IV.) Nitro-hydrochloric acid contains Chlorine, which is an oxidizing agent, and probably exerts in the blood an action of this kind. It is clear that it is capable of retarding the formation in the system, and deposit in the urine, of lithic acid and oxalate of lime; though its modus operandi is not determined with certainty. This question is of some theoretical importance, and will soon be considered at some length.
Among Antiscorbutics, Potash and its salts have been already shown to affect the blood. Their efficacy in scurvy is, however, a disputed point. That of Lemon-juice is established. It contains Citric acid and Potash; the former in great excess. Now either of these by itself would, in cases requiring it, and given in small doses, act as a Restorative. In large doses, Citric acid would disturb the reaction of the secretions, and Potash would impoverish the blood. When both together, the Citrate of Potash would undergo oxidation, and thus exert an operation in the blood of a refrigerant kind. Similar materials occur in most fresh vegetables.
Antiperiodics are medicines which are used in the cure of Ague, and of other periodic diseases, on the Catalytic principle. Tonics are used in the same diseases on the Restorative plan; but their utility extends also to other cases on the same grounds. Arsenic is the most potent of Antiperiodics. The Terchloride, and the Arsenite of Potash, are the preparations most frequently employed. Arsenic produces an evident action in the blood. When given in slight excess, it is apt to bring on œdema of the face, and redness of the conjunctivæ. Besides causing various nervous disorders when in large doses, its continued use may bring on a cutaneous eruption, described by Mr. Hunt as a kind of pityriasis, together with a failure of appetite, general depression, a quick small pulse, hurried respiration, and sometimes swelling of the feet. Any kind of eruption would alone constitute sufficient proof of an operation in the blood.
The metallic salts used as Anticonvulsives are all capable, when taken for some time, of causing a deterioration of the blood. This is most apparent in the case of Lead, which, besides a number of nervous symptoms, tends to bring on a kind of jaundice, with general wasting of the body. Chronic poisoning by Zinc and Copper resembles that by Lead. The symptoms of what is called "Zincal intoxication" were recently described to the French Academy by M. Landouzy of Rheims, as occurring constantly among the zinc-workers. There was sometimes an œdema like that produced by Arsenic.
The production of all the known nervous disorders by the presence in the blood of different metallic medicines, gives a strong additional probability to the belief that these disorders, when occurring spontaneously, are in many cases due to the presence in the blood of some unknown poison.
Among Antisquamics, the last Catalytic order, we meet with Arsenic again. Common Pitch is of almost equal utility in Lepra. It has some action in the blood, due to some one of its bituminous principles; but this action is not well made out, or understood. Sulphur, besides its use externally in Scabies, is administered internally with advantage both in this and some other skin diseases. It effects changes in the blood, inasmuch as it is found to combine there both with hydrogen and oxygen, and to carry them out of the system as sulphuretted hydrogen and sulphuric acid. Dr. Pereira and others ascribe to Sulphur a resolvent and liquefacient action.
Thus it is sufficiently shown that all of these medicines work out a certain process or operation in the blood, and affect the condition of that fluid. But I am very far from believing that this known operation is in all cases the one by which they neutralize morbid poisons. This action is probably of a much more inscrutable character.
Before proceeding further, I may here take the opportunity of insisting again on the differences between Catalytic and Restorative medicines. Catalytics will even in health work out their peculiar process in the blood. Restoratives exercise in that case no particular influence. The latter may remain in the blood; their office is supply or substitution. Catalytics may not remain beyond a certain time; their office is counteraction. The system then labours to excrete them. Before passing out of the body, one or two, as Colchicum, may act on the nerves. In the moment of excretion, the majority act as Eliminatives. But some, as the metals used as Anticonvulsives, are astringent, and diminish secretion generally. Mercury, Antimony, and Iodine, are among the most important Eliminatives known. They act on all glands, but on some more than on others. Antimony is also a special sedative to the Vagus nerve, and as such exerts an important influence, which enables it sometimes to cut short the process of inflammation by depressing the action of the heart.
We now arrive at the third minor proposition.