The action of aconitin on the dog's heart, therefore, seems to consist in:

1. A stimulation of the inhibitory mechanism, especially of the centres in the medulla oblongata.

2. An increase in the irritability of the muscle of the auricle and the ventricle, which leads to independent contractions of one or both of these divisions and culminates in fibrillary contractions in the ventricle.

The first of these is the only effect seen in the therapeutic use of the drug, and aconitin may, therefore, be considered to be indicated when it is desirable to stimulate the inhibitory centre without acting on the heart muscle. Of course it has a further effect on the circulation through the stimulation of the vaso-motor centre, but this would appear to be of minor importance.

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