60 GENERAL ACTIONS OF DRUGS 



Tonics. — The word " tonic " is another term even more 

 vague and all-embracing than " alterative," and, therefore, 

 more difficult to accurately define. Tonics improve the 

 general nutrition and health, and, as ordinarily understood, 

 refer to drugs promoting appetite and digestion (bitter 

 tonics, as gentian) ; the state of the blood (hsematinics, as 

 iron and arsenic) ; or the condition of certain organs (heart 

 tonics, as digitalis ; nerve tonics, as strychnine). 



Tonics are indicated in the treatment of debility (gen- 

 eral or special) and anaemia. 



Drugs Influencing: Bodily Heat. 



Antipyretics are drugs lowering the temperature of the 

 body in fever. The mechanism concerned with temperature 

 changes is as follows : 



(1) Heat production. — There is a centre in the corpus 

 ^ striatum for heat production. Probably this controls mus- 

 cular activity, which is chiefly instrumental in the production 

 of bodily heat. 



(2) Heat loss. — There is a centre for heat dissipation 

 situated in the medulla. This controls the vasomotors and 

 state of vascular tension ; the activity of the sweat glands 

 and respiration ; and, therefore, the amount of heat lost by 

 radiation from the blood vessels of the skin, by evaporation 

 of sweat, and by the act of respiration. Heat is also lost 

 by the passage of faeces and urine. 



(3) Heat regulation. — There are heat-regulating centres 

 in the cortex cerebri (?) which coordinate or adjust the 

 relations existing between the heat-producing and heat- 

 dissipating centres. 



Finally, the bodily temperature is reflexly influenced by 

 sensory impulses originating in various parts of the body, 

 and conveyed by afferent nerves to the three brain-centres 

 controlling temperature. Agents lowering bodily tempera- 

 ture in fever may act to depress the heat-producing centre ; 

 to stimulate the heat-dissipating centre ; to dilate vessels ; 



