Arsenic is used in Ague and intermittent disorders, and acts on the Catalytic principle, but it is not serviceable in the other cases in which Quinine is used. It is not a Tonic, nor does it seem to have any relation to the function of the liver. I have thought it advisable to restrict the term _Antiperiodic_ to the _Catalytics_ which are used in Ague. (_Vide_ p. 141.) Quinine and Arsenic may both be employed in all disorders which put on an intermittent or periodic type. The chief of these is Ague, or Intermittent Fever. It is perhaps easier to arrest the disorder by Quinine than by Arsenic; for Quinine may be given in large doses, which cannot be done with Arsenic. But the administration of the latter may be continued during the paroxysm, when the great febrile reaction forbids the use of the other. The dose of Quinine is apt to disagree with an irritable stomach, and to increase the fever. It is generally laid down that this remedy should not be administered when there is a quick hard pulse, or heat and dryness of the skin. Some, however, have lately ventured to prescribe it to patients in high fever. It appears that there is a particular class of patients which in such cases will bear the administration of Quinine with impunity; while others are unfavourably affected by the smallest dose. It is perhaps at all times advisable to arrange so that the medicine shall, if possible, be taken after meals, for it is less likely to irritate a full stomach. And when it is thought proper to give it to a patient in fever, a small dose of Tartar Emetic or Ipecacuanha should be conjoined with it--not, of course, sufficient to produce vomiting, but so that an increase of the febrile excitement may be prevented. Quinine is in all cases better tolerated by the stomach when the dose is considerably diluted with water. A combination of Quinine and Iron is often of great service in feeble and relaxed conditions, where there is co-existent Anæmia. (_Vide_ p. 129.) IRON. Class I. Div. I. Ord. V. CHALYBEATA. It has been shown, in the article on Chalybeates, that the action of Iron is of a distinctly Restorative nature. There is in the blood a red colouring matter, called Hæmatosin. It is found by chemical analysis that Iron is an essential part of this substance. The existence of the right amount of Hæmatosin in the blood is of vital importance. It is contained in the red globules of the blood. When it is diminished in quantity, the number of these red globules is lessened in the same proportion. This produces a paleness of all the tissues, an inactivity of the muscular fibre, an impairment of all the animal functions, and a general languor and debility of the whole frame. This is Anæmia.