In the second case the poison, whether applied direct to the eye or entering the circulation by subcutaneous injection, contracts the pupil; the contraction persists if the eye is extirpated, but in all cases the contraction may be changed into dilatation by the use of atropine. An example of this kind of myosis is the action of muscarine. It is dependent on the stimulation of the ends of the nerves which contract the pupil, especially the ends of the _nervus oculomotorius_ supplying the sphincter iridis; this form of myosis is called _myosis spastica periphera_. A variety of this form is the _myosis spastica muscularis_, depending on stimulation of the musc. sphincter iridis, seen in poisoning by physostigmine. This causes strong contraction of the pupil when locally applied; the contraction is not influenced by small local applications of atropine, but it may be changed to dilatation by high doses. Subcutaneous injection of small doses of physostigmine does not alter the pupil, but large poisonous doses contracts the pupil in a marked manner. =Toxic mydriasis, or toxic dilatation of the pupil.=--The following varieties are to be noticed:-- 1. Toxic doses taken by the mouth or given by subcutaneous injection give rise to strong dilatation; this vanishes before death, giving place to moderate contraction. This form is due to stimulation of the dilatation centre, later passing into paralysis. An example is found in the action of aconite. 2. After subcutaneous or local application, a dilatation neutralised by physostigmine in moderate doses. This is characteristic of β-tetrahydronaphthylamine. 3. After subcutaneous injection, or if applied locally in very small doses, dilatation occurs persisting to death. Large doses of physostigmine neutralise the dilatation, but it is not influenced by muscarine or pilocarpine: this form is characteristic of atropine, and it has been called _mydriasis paralytica periphera_. The heart at the height of the poisoning stops in systole. =2. Arrest in systole.=--The systole preceding the arrest is far stronger than normal, the ventricle often contracting up into a little lump. Contraction of this kind is specially to be seen in poisoning by digitalis. In poisoning by digitalis the ventricle is arrested before the auricle; in muscarine poisoning the auricle stops before the ventricle. If the reservoir of Williams’ apparatus is raised so as to increase the pressure within the ventricle the beat may be restored for a time, to again cease.