Drugs Acting On The Motor Centres Of The Brain

To investigate these, the motor area of the cortex is exposed by trephining, and the strength of current which it is necessary to apply to the motor area to produce corresponding movements, is noted before and after the administration of the drug. Another method is to observe the strength of current necessary to evoke a movement, then to allow the wound made by the trephine to close, afterwards the animal is made to take the drug regularly for some weeks. The opposite motor area is then exposed, and the strength of current required to call forth movements is noted.

It has been found that the following diminish the activity of the motor area.

(1) Alcohol.

(2) Anaesthetics.

(3) Chloral hydrate.

(4) Potassium bromide.

(5) Sodium bromide.

(6) Ammonium bromide.

Bromides are largely used in epilepsy and other convulsive disorders on account of this function.

Drugs exciting the motor cells of the cortex are -

(1) Atropine.

(2) Absinthium.

(3) Strychnine.

(4) Physostigmine.

They have no therapeutical application in virtue of this property.

General Cerebral Stimulants

It is impossible to know anything of these by experiments on animals. In man they cause general excitation of the mental faculties, followed in many cases by delirium and incoherence. The exact form of delirium differs a little in each case.

Such drugs are -

(1) Belladonna.

(2) Stramonium.

(3) Hyoscyamus.

(4) Alcohol.

(5) Chloroform.

(6) Ether.

(7) Nitrous oxide.

(8) Coffee.

(9) Tea. (10) Guarana.

(11) Coca.

(12) Cannabis Indica.

(13) Lupulus.

(14) Opium.

(15) Camphor.

(16) Santonin.

(17) Quinine.

(18) Salicylic acid.

(19) Tobacco.


Many of these are taken habitually as cerebral stimulants; for example, alcohol, tea, coffee, tobacco, in England; opium in the East; cannabis indica in many parts of Asia; coca in parts of South America; and if it is wished to give a cerebral stimulant as a drug, one of these is usually chosen. The rest, which are very important, are commonly employed for some other action. With very many of this class of drugs, as will be seen directly, the stimulant action soon gives way to a paralyzing influence.

General Cerebral Depressants

These are commonly divided into three classes: Hypnotics or Soporifics, Narcotics and Anaesthetics.

Hypnotics or Soporifics are drugs which produce sleep, closely resembling, if not identical with, natural sleep. The brain during sleep is anaemic, and it is thought that this anaemia is the cause of sleep; possibly some soporifics act by producing cerebral anaemia.

The hypnotics are -

(1) Opium.

(2) Morphine.

(3) Chloral hydrate.

(4) Chloralamide.

(5) Butyl-chloral hydrate.

(6) Bromides.

(7) Trional.

(8) Pellotine.

(9) Sulphonal.

(10) Paraldehyde.

(11) Alcohol.

(12) Hyoscine.

(13) Cannabis Indica.

(14) Urethane.

(15) Lupulus.

(16) Lactucarium.


These drugs are often used for persons suffering from sleeplessness, but it is far more important to remove the cause of the sleeplessness. Sleep is often promoted by dilating the vessels of other parts of the body than the brain; for example, a warm bath or an abundant meal conduces to sleep. The use of hypnotics is greatly abused. Those who take them become habituated to them, so that at last even large doses do not cause sleep. Chloral hydrate if used with great caution, pellotine, paraldehyde, trional, and chloralamide are perhaps the most satisfactory.

Narcotics are substances which not only produce sleep, but also in large doses depress the functions of respiration and circulation. Many of them fall also under the head of general anaesthetics; others are, in smaller doses, hypnotics. All must be given in considerable doses.

The following is a list of them.

(1) General Anaesthetics.

(2) Opium.

(3) Chloral hydrate.

(4) Belladonna.

(5) Stramonium.

(6) Hyoscyamus.

(7) Alcohol.

(8) Cannabis Indica.

(9) Lupulus.

All must be given in considerable doses.


They are of great use in calming excitement of any kind; many of them, such as, for example, opium and belladonna, are beneficial in relieving distress and producing sleep in heart disease.