CAFFEINE 397 



one-half drachm in a cup of the beverage, has no physiolo- 

 gical action except to disturb digestion and cause bilious- 

 ness. This result is not in accord with the general belief, 

 and it is probable that caffeine possesses a transient action 

 in stimulating intestinal peristalsis, the cerebral functions, 

 and in lessening vascular tension. 



Circulation. — Caffeine stimulates the heart muscle and 

 vasomotor centres. The action of the heart is ' strengthened 

 and accelerated after moderate doses in most cases. Some- 

 times the stimulating action on the vagus centre overcomes 

 that on the heart and the pulse is somewhat slowed. Blood 

 tension is enhanced. In poisoning the pulse becomes weak 

 and irregular and the heart stops in diastole. 

 * Nervous Systerfi. — Caffeine is a certain and direct stim- 

 ulant to the higher nervous centres. In moderate doses it 

 produces wakefulness and restlessness (action of tea and 

 coffee at night on man), and increases the capacity for 

 mental and physical work (see muscles). In the lower ani- 

 mals caffeine often causes the most intense cerebral exdite- 

 ment and mania in large doses. The alkaloid affects the 

 spinal cord like strychnine, and toxic quantities produce 

 restlessness, increased reflex excitability and convulsions in 

 the lower animals. It is undetermined whether the convul- 

 sions are of cerebral or spinal origin. The motor and sensory 

 nerves are unaffected by medicinal doses. Caffeine opposes 

 the depressaftt action of opium and alcohol. It antagonizes 

 alcohol in stimulating the highest or controlling functions 

 of the brain, the reasoning faculties, perception of sensory 

 impressions and association of ideas, and greater accuracy 

 of touch and capacity for physical exertion. 



Muscles. — The injection of caffeine solution into a frog's 

 leg causes a stiffness and hardness of the muscles lilte that 

 seen in rigor mortis. On muscle fibres, removed from the 

 body, it acts in the same way by coagulating the muscle pro- 

 teids. In small quantities in the body it acts to stimulate 

 the ability of the muscle to contract and its capacity and en- 

 durance for work. The action of tea and coffee, in enabling 

 men to perform more physical work, has hitherto been 

 ascribed to the action of caffeine on the nervous system, but 

 is now attributed to its effect on the muscles themselves. 



Kidneys. — The kidneys primarily contract for two or 

 three minutes' with corresponding diminution in the flow of 



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