DRUGS ACTING ON THE NEIIVOUS SYSTEM 37 



(b) Drugs acting systemically to dilate vessels, j ; 



Amyl nitrite Chloral 



Nitroglycerin Aconite 



Spirit of nitrous ether Opium 



Alcohol Belladonna (secondary action) 



Ether Hyoscyamus " 



Chloroform Stramonium * ' 



(c) Agents acting locally to contract vessels. 

 Cold Astringents 



(d) Agents acting locally to dilate vessels. 

 Heat Counter-irritants 



Uses. — Drugs or agencies causing general dilatation of 

 vessels are useful in overcoming internal congestions and 

 colds by equalizing the circulation ; that is, by causing the 

 blood to be distributed more equably about the body. They 

 are also of benefit in morbid conditions attended with a 

 high, vascular tension; and are serviceable in dilating 

 peripheral vessels and in causing perspiration and loss of 

 heat in fevers (spirit of nitrous ether and alcohol). Drugs 

 inducing general contraction of vessels are employed in 

 disorders characterized by loss of tone, as in shock and 

 collapse ; and in heart weakness or disease (digitalis and 

 strychnine) ; also in internal haemorrhage and inflammations 

 (ergot) ; and to aid the absorption of dropsies and cede mas. 

 The uses of drugs locally contracting vessels will be 

 described under Astringents (p. 63) and of agents locally 

 dilating vessels under counter-irritants (p. 62). 



Drugs Acting on the Nervous System. 



I. — Drugs Influencing the Brain. 



It is impossible to classify drugs according to their 

 action on the various centres of the brain, because our 

 knowledge is insufficient. In a general way, drugs affect- 

 ing the nervous system fall into two groups,— the excitant 

 and depressant. But another difficulty arises in regard to 



