These are drugs which cause sneezing and increased secretion from the nose when locally applied to it. The drugs must be in a pulverised condition. The chief are :Tobacco (snuff). Veratrum album. Ipecacuanha.

Euphorbium. Sassy bark. Saponine.

Irritation applied to the nose is transmitted by the nasal branches of the fifth to the respiratory centre in the medulla oblongata, and excites the sudden and forcible expiratory movements of sneezing. At the same time, however, the stimulus is transmitted to the vaso-motor centre, and the blood-pressure becomes considerably increased by the contraction of small vessels throughout the body, even when no sneezing occurs. When sneezing takes place, the pressure is still further increased by the muscular efforts which occur in the act. It is probable that there is not only general rise in blood-pressure but also that local dilatation of the cerebral vessels is reflexly produced by the nasal irritation, and thus a stimulant effect is produced on the brain. Snuff is therefore employed as a luxury giving a feeling of comfort and enabling the snuff-taker to think more clearly - 'clearing the head ' as it is often termed (vide p. 193).

Uses

Though comparatively little used now, sternutatories were formerly employed in failure of memory, deafness, and severe persistent headache. From the violent expulsive efforts which they induce, they were given also to cause the expulsion of foreign bodies from the air-passages, and to hasten the expulsion of the child in cases of lingering labour where no obstruction was present, but where expulsive force was deficient. They were given also in order to try and check diseases at the commencement, by what was termed 'shock to the system.'

One curious thing is to be remarked, that stimulation of one part of the respiratory tract may arrest abnormal actions in another. Thus Marshall Hall has shown that actual sneezing may frequently be prevented, after the inspiration by which it is usually preceded has occurred, by forcibly rubbing the end of the nose or by tightly compressing the nostrils. In a similar way irritation of the interior of the nose by snuff will sometimes arrest obstinate hiccough.

Contraindications

On account of the high blood-pressure which they produce their use is by no means free from danger in persons affected with atheroma or a tendency to pulmonary haemorrhage or apoplexy, as they may cause rupture of a vessel, and in those who suffer from hernia or from prolapsus of the uterus, they may seriously increase the gravity of these affections.

Respiratory Sedatives.

These are substances which diminish cough and spasmodic difficulty of breathing.

They may be divided into drugs which (1) Tend to remove the irritation which acts as the exciting cause of the cough.

(2) Tend to lessen (a) the afferent nerves in the lungs; irritability of (b) the respiratory centre.