The drugs which act on the circulation have been divided according to their action into stimulants, tonics, and sedatives. Each of these classes has been further subdivided into cardiac and vascular, according as its members act on the heart and vessels. There are thus six subdivisions in all: cardiac stimulants, vascular stimulants, cardiac tonics, vascular tonics, cardiac sedatives, and vascular sedatives.

Cardiac Stimulants

These are substances which rapidly increase the force and frequency of the pulse in conditions of depression. The most important are ammonia, and alcohol in its various forms, but there are also other substances which are sometimes useful.

Heat.

Liquor ammonia?. B.P. Aqua ammoniae. U.S.P. Ammonium carbonate. Sal volatile (spiritus ammoniae aromaticus). Alcohol. Brandy. Whisky.

Eau de Cologne. Gin.

Liqueurs. Strong wines. Atropine.

Ether. Chloroform. Spirit of chloroform. Spirit of ether. Camphor.

Aromatic volatile oils. Oil of turpentine. Heat and counter-irritants to the prsecordium.

Cardiac stimulants are used to prevent or counteract sudden failure of the heart's action in syncope or shock due to mental emotion, physical injury, or poisoning by cardiac depressants, or by the bite of snakes, or when the action of the heart becomes much depressed in the course of fevers or other diseases.

Although alcohol after its absorption stimulates the heart, yet its effect on the heart is probably, to a considerable extent, due to a reflex action on it through the nerves of the mouth, gullet, and stomach. Its action is consequently very rapid, and begins before there has been time for much of it to be absorbed. On this account, however, it must be given in a somewhat concentrated form, and if much diluted, as in the form of weak wine or beer, which has little or no local action and can exert no reflex action, it has little or no power as an immediate stimulant. When given in disease it is best to administer it in small quantities frequently, and the rule by which to ascertain whether it is doing good or not is: Does it bring the circulation more nearly to the normal or not ? If it does so, it is beneficial; if it does not, it is harmful. Thus, if the pulse be too quick, alcohol should render it slower; if already abnormally slow, alcohol should make it quicker. If too small, soft, and compressible, alcohol should render it larger, fuller, and more resistant. There are other rules connected with the effect of alcohol on other organs which also regulate its use in'disease, but these will be given further on.

Ether alone or mixed with alcohol has a stimulant action almost more rapid than alcohol itself; and chloroform in small doses, and especially when mixed with alcohol, is also a powerful stimulant.

Ammonia has not only a reflex action on the heart like that of alcohol, but has powerful stimulating action on the vaso-motor centre. Its action when applied to the nose in syncope has already been discussed. In cases of snake-bite thirty minims of liquor amnioniae have been injected directly into the veins. The immediate stimulating effect appears to be beneficial, although it is doubtful whether life can really be saved by this means.

Camphor is useful as a cardiac stimulant in febrile conditions with a tendency to failure of the circulation, as in typhus and typhoid fevers; in exanthemata, when the rash does not appear; in asthenic pneumonia, and in the typhoid condition depending on other diseases.

Aromatic volatile oils and substances containing them have also been used in similar but less severe conditions.

One of the most powerful of all cardiac stimulants is heat, and when the heart's action threatens to fail it may be frequently restored by warm fluid taken into the stomach, or by the application of an indiarubber bag1 or bottle filled with hot water, or of a bag filled with hot sand or salt, or of a hot poultice to the cardiac region.

1 An indiarubber bag for holding hot water is one of the most useful things an invalid can carry about with him. It should have a flannel case fastened by buttons

It must be remembered that the high temperature of the body in febrile conditions acts as a cardiac stimulant; and if this stimulus be removed by the temperature falling, either in the natural course of the disease or in consequence of the administration of antipyretics, the heart may fail and collapse, and death ensue, unless it be stimulated either by medicines or by the application of heat to the cardiac region.