_Skin diseases_ are no doubt connected with some disorder in the blood. We might almost presume this from the analogy of the known blood-poisons, by nearly all of which an eruption may be produced. The eruptive fevers, which run a certain course, depend upon contagious poisons; but they are not under the influence of Antisquamic remedies. These are serviceable in a class of disorders, of each of which a cutaneous eruption is the most apparent, or the only obvious symptom. The true squamous disorders are Lepra vulgaris and Psoriasis vulgaris. The causes of Impetigo, Porrigo, and Scabies, are probably similar to those of the true squamæ, for they are often curable by similar remedies. The actual eruption of Porrigo is accompanied by a parasitic fungus, which may sometimes be transmitted from one person to another; and a small insect or Acarus which haunts the vesicles has been alleged as the cause of Scabies; but it is not, after all, quite clear whether these attendants may not be merely the concomitants or the results of these two disorders. At all events, Lepra and Psoriasis are true blood diseases, and are often inherited. They are more obviously under the influence of Antisquamics than the other skin diseases. It has thus been shown that the diseases in which Catalytics are used are each to be accounted for by a process in the blood. The fourth minor proposition will not be so difficult to establish as the last, although it is in fact the most important of all. _The action of a Catalytic results in the neutralization or counteraction of one or more of these morbid agencies._ This has already been sufficiently proved. It is established by experience that these remedies severally counteract the diseases named. They have been shown to have an action in the blood; and the diseases have been proved to be blood-diseases. Thus it is clear, that if the former counteract the latter, and have no action on the nerves, they must do it by some agency in that fluid, over the particles of which both exert an influence. They are Catalytic Hæmatics; _i.e._, medicines which, by an operation in the blood, are enabled to counteract disorders which depend upon active morbid agencies. This is all that can be positively affirmed of their mode of operation. The fifth and last minor proposition relates to an important difference between these and Restorative medicines.--The latter may remain in the system, for if they did not do so, they could restore nothing to the blood. But Catalytics cannot restore any thing, for they are generally unnatural to the blood. They must sooner or later be excreted. _Catalytics are unnatural to the blood, and must at length pass out of the system._