The condition of Debility, whatever its proximate cause, seems always to be traceable in the first place to a want in the blood, which interferes with the due exercise of their functions by the nerves and other organs, by impairing their nutrition. It follows fevers, and accompanies chronic diseases, in both of which cases the blood has been exhausted by continual waste and excretion, without the maintenance of a proper supply. In cancerous, scrofulous, scorbutic, and dyspeptic habits, the blood may be deteriorated by a fault in the assimilative processes. When in these instances there is marked Anæmia, iron may be of most service; but when the blood is poor without any apparent deficiency of red colouring matter, then are bitter Tonics needed to improve its condition, and form a valuable adjunct to the special remedies that the case may require. They ought not, as a general rule, to be administered in high fever, or when the pulse is hard, the tongue coated, or the stomach irritable. A loss of appetite, a nervous headache, a soft compressible pulse, a quivering tongue, a flabby condition of the muscles, with general inertia and indisposition to exertion, are indications for their employment. In some cases emetics and antimonials, in others mild purgatives, are of use in preparing the system for their reception. It seems then that Debility is to be attributed generally to the state of the blood; and is to be cured by improving it. By so doing we may communicate tone to the muscular system, improve the appetite, and increase the nervous force. Ague, or Intermittent fever, is also a blood-disease. If it were only from the analogy of other fevers, we might infer this. But there are more particular proofs. This disorder is caused by the exposure of the system to a certain peculiar poison or miasm, which is generated in the ground in certain places, and subject to known laws. The result of the influence of this miasm is a process in the blood which has been compared to fermentation, and which produces regularly recurring paroxysms of a peculiar kind. There is apparently some disturbance in the great calorifacient process, in which the blood is concerned, and not the nerves. Each fit commences with shivering; there is then a hot stage; and finally sweating. The attack then goes off, seemingly as if the poison that caused it were eliminated in the perspiration. But it is not all gone. After working in the blood for a definite period, most commonly two days, it again breaks out, and the same train of symptoms recurs. Thus this strange disorder, both in its origin and in its progress, appears to be seated in the blood. So also are its results evidenced there. Continual Ague deteriorates that fluid, causing general anæmia, and producing more or less enlargement of the spleen, which could only be brought about by some faulty condition of the circulation.