The action of atropine in dilating the pupil is also aided by a stimulation of the fibres from the sympathetic nervous system, which innervate the remaining muscle of the iris - the dilator pupillae.
Hypodermic tabloids of morphine sulphate either alone or combined with atropine are much in use.
In small therapeutic and in small toxic doses atropine stimulates the motor apparatus of the spinal cord, just as it stimulates the centres in the medulla oblongata.
The action of atropine on the motor nerves is equally important.
Thus atropine will save life after three and a half times the fatal dose of physostigmine has been taken, but will hasten the end if four or more times the fatal dose has been ingested.
Toxic doses of atropine - and therefore of belladonna - raise the temperature several degrees.
A twentieth, even a tenth of a grain of atropine sulphate should be injected subcutaneously, the drug being a direct stimulant of the respiratory centre.
The use of atropine is absolutely contra-indicated in any case where the intra-ocular tension already is, or threatens to become, unduly high.
So valuable are certain of the properties of atropine that it is often desirable to give doses of one-twentieth or onetenth of a grain; but these will never be ventured upon by the practitioner who is ignorant of the great interval between the minimum toxic and the minimum lethal dose.
It follows from the above that a patient who is definitely under the influence of atropine will display rapid pulse, dilated pupils, a dry skin and a sense of discomfort, due to dryness of the mouth and throat.