MOTOR STIMULANTS. 497 



possibly other drugs, heat and cold, electricity, properly 

 regulated pressure, and section or stretching of the nerves are 

 different means of removing sensibility or at least pain. 



d. The sensitive and perceptive centres in the cerebrum may 

 be the seat of action of anaesthetics. Amongst the substances 

 possessing this effect are Opium, Chloral, Chloroform, Ether, 

 and Cannabis Indica, consciousness as a whole being affected by 

 these measures, which are called general anaesthetics, general 

 anodynes, or narcotics a series of titles which will be 

 presently noticed. Lastly, it will be observed that certain sub- 

 stances, such as Opium, arrest the afferent impressions at every 

 point at their formation, in the course of their conduction, and 

 where they impinge upon the sensorium, that is, they act upon 

 the sensory tract from one extremity to the other. 



e. The special senses also can be directly influenced by 

 various measures, including drugs. Local anaesthetics reduce 

 the keenness of the sense of touch. Deafness and subjective 

 noises are produced by Quinia, Salicylic Acid, and Alcohol. 

 Santonin causes green vision. Taste is excited by a variety of 

 influences which we have already studied ; depressed and 

 peculiarly disturbed by Aconite and other alkaloids. 



2. Motion. Our command of the motor side of the 'nervous 

 system is greater than our influence over sensation, for the 

 reason that motor parts can be acted on not only directly, but 

 also reflexly through sensory parts, as we have just seen local 

 irritants exciting muscular movements, and local depressants 

 arresting them. 



a. Motor stimulants are specially interesting, as different 

 drugs act on different parts of the motor apparatus from the 

 cerebrum to the muscles. Alcohol, in moderate doses, increases 

 the activity of the " motor " convolutions, and so probably do 

 Chloroform and Ether for a very short time. The medulla, as 

 the centre of the respiratory movements, is excited by 

 Strychnia, Ammonia, Belladonna, and by small doses of Alcohol, 

 Ether, and Chloroform. The anterior cornua of the cord (pro- 

 bably in association with the posterior cornua) are powerfully 

 stimulated by Strychnia convulsions being readily induced. 

 Stimulation of the motor nerve-trunks can be used to excite the 

 muscles by means of faradaic electricity. 



Our most valuable motor stimulants, however, are applied to 

 the terminations of the nerves, the terminal apparatus, and the 

 muscles themselves, in the form of local motor stimulants. 

 Strychnia acts also in this way. Electricity is in constant use 

 for this purpose as the faradaic, occasionally as the galvanic, 

 current. Passive movements of the limbs, rubbing, sham- 

 pooing, and douching, by rousing the local circulation and 

 2 G -8 



