_b._ Rasori and other Italians adopted a similar idea about the commencement of this century, only that they supposed two contrary agencies, instead of variations in the degree of the same action, like the Brunonians. Giacomini classified medicines on this plan. The two classes of medicines are termed "Hypersthenics," and "Hyposthenics,"-- _i.e._ Stimulants, and Contra-stimulants, or Sedatives. These were to be used respectively in asthenic and in sthenic disorders. But this idea did not originate with these physicians. It prevails among the modern Hindoos, and seems to have been inculcated by certain medical writers of that nation in very remote times. (_On the Hindoo System of Medicine, by Dr. Wise_, 1845, p. 213.) _c._ The last-mentioned idea supposes only one kind of opposition, and therefore only two descriptions of diseased action. But a much more plausible notion than that is, that each particular disease or symptom is to be cured by administering a remedy which is capable of producing a contrary state. By this contrary condition the disorder is to be neutralized. This was the maxim of Hippocrates--[Greek: ta enantia tôn enantiôn estin iêmata]--"contraries are the remedies of contraries." (De Flatibus, par. iii.) On this principle we give purgatives in constipation, opium in diarrh[oe]a, sedatives to relieve pain, sudorifics to combat dryness of skin, etc. etc. But the rule becomes inapplicable when the cause of disease is so complicated that we cannot tell where to find a substance that shall directly oppose its agency. Besides, it cannot in theory be universally applied, for it takes no notice of treatment by evacuation or by revulsion. _d._ I am brought now to an idea which is directly opposed to the last. The rule of the disciples of Hahnemann is, "Similia similibus curantur"--or, diseases are to be cured by remedies which shall produce effects similar to them. Now if this were the case, the majority of disorders would be hopelessly incurable. We know of no medicines that are capable of producing such affections as ague, small-pox, or phthisis; and when such remedies are known, their employment would certainly be singularly objectionable. Who would administer Strychnia in tetanus, Opium in congestion of the brain, or irritants in Gastrodynia? The arguments alleged in support of the theory are of the most fallacious kind. For example, it is said that diaphoretics cured the sweating-sickness, and purgatives are given with advantage in diarrh[oe]a, on the "Hom[oe]opathic" principle. But it should be observed that the sweating in one case, and diarrh[oe]a in the other, are the attempts of nature to get rid of the disease by eliminating a poison; and that in seconding these attempts we are availing ourselves of an agency which does not resemble the disease, but is like to the natural mode of cure. Such treatment depends, in fact, upon the principle which will have to be considered next in order.