_The diseases in which these medicines are employed are active blood-diseases._ This consideration need not detain us long, for in most cases the correctness of the statement is universally admitted. _Inflammation_ may be produced by a variety of blood-poisons, in each of which instances it partakes of a special character. Thus there are the syphilitic, scrofulous, and rheumatic inflammations. Simple inflammation may be caused by the injury of any part or organ, external or internal. It commences in the capillary vessels, and, if extensive, affects the blood generally, and produces fever. The blood then contains an excess of Fibrine, causing it, on coagulation, to exhibit the "buffy coat." There are also found in this, according to Mulder, some peculiar hyperoxides of Proteine. The colourless corpuscles are in excess; and among the red corpuscles is observed a peculiar tendency to arrange themselves together in rows. This is doubtless in some way connected with the morbid process going on in the blood. _Syphilis_ is evidently traceable to a special poison. This is recognised by the fact of its communication from one person to another. In the system of the infected person, if left alone and uncontrolled, it breeds and increases in quantity, works out all the mischief that it is capable of effecting, and may again be propagated to others, either by inoculation into the blood, or by an equally direct transmission to a tainted offspring. _Scrofula_ is also a blood-disease. All its manifestations are explainable on such a supposition. It is transmissible from parent to child; and it holds good as a general rule that hereditary diseases are seated in the blood. It is unaffected by any of those medicines that act only on the nerves. It produces a deterioration of the blood. _Arthritic_ disorders are always accompanied by a change in the blood. In Diabetes grape-sugar is present there in large quantities, and has to be excreted by the kidneys. Similarly, in Oxaluria, oxalic acid is found there; in Lithiasis, lithic acid in excess. In Rheumatic fever there are profuse sweats, in which the natural acid of the perspiration is enormously increased in quantity. It is stated by Berzelius to be lactic acid. Either this, or some other acid like it, must be formed in excess in the blood. In Gout we have sometimes a deposit of urate of soda in the cellular tissue opposite the small joints. The same salt has been occasionally found in the urine in Gout. Lastly it has been detected in the blood in that disorder by Dr. Garrod, and since him, by Dr. Bence Jones. (_Animal Chemistry, p._ 29.) Thus, in all these disorders there is a wrong in the blood.