38 GENERAL ACTIONS OF DRUGS 



classification from the fact that the same drug usually both 

 excites and depresses. Probably all drugs influencing the 

 nervous apparatus possess some exciting action, and most 

 drugs which excite in small doses cause depression and 

 paralysis after poisonous quantities. 



For example, alcohol, ether and chloroform are cerebral 

 excitants in small doses, but in large doses are depressants 

 (hypnotics) and paralyzants (anaesthetics). Belladonna and 

 its congeners, on the other hand, only excite the brain in 

 large amounts ; while opium and cannabis Indica may excite 

 the brain in small doses, but are used for their more common 

 depressant action. The condition of the patient has some 

 bearing on the action of a drug influencing the brain. Thus 

 moderate doses of alcohol depress and stupefy healthy 

 animals while stimulating the enfeebled and ill-nourished. 



The brain of the lower animals is undeveloped compared 

 to that of man, and, in accordance with the general fact that 

 the more highly a portion of the nervous mechanism is 

 organized the more powerfully is it influenced by drugs, it 

 follows th:it drugs actiug on the brain and cord are more 

 prone to aff'ect the cord in veterinary patients, while impres- 

 sing the brain more potently in man. 



We shall be content to classify drugs acting on the 

 nervous system according to their most pronounced action 

 in moderate doses. 



(a) Cerebral Excitants. 



Alcohol Caffeine 



Anaesthetics Quinine 



Camphor Cocaine 



Uses. — These drugs are rarely used simply to excite the 

 brain, but forjother purposes. Camphor, caffeine and quinine 

 are employed to generally excite the nervous system in 

 depressed conditions. Caffeine is a valuable antidote to the 

 depressing cerebral action of opium in poisoning. 



(b) Cerebral Depressants. — It is fortunate that drugs 

 progressively paralyzing the functions of the brain follow 

 the so-called law of dissolution — i.e., paralyze the various 



