394 VEGETABLE DRUGS 



the oil (caffeone), of which there is from one to one-half dram in a cup 

 of the beverage, has no physiological action except to disturb digestion 

 and cause biliousness. This result is not in accord with the general 

 belief, and it is probable that caffeone possesses a transient action in 

 stimulating intestinal peristalsis, the cerebral functions, and in lessening 

 vascular tension. 



Circulation. — Caffeine stimulates the heart muscle and vaso-constric- 

 tor centre. The action of the heart is strengthened and accelerated after 

 moderate doses in most cases. Sometimes the stimulating action on the 

 vagus centre overcomes that on the heart and the pulse is somewhat 

 slowed. Blood tehsion is enhancedj but the coronary, pulmonary and cere- 

 bral arteries are dilated, because of absence of constrictor nerves and 

 increase in general blood pressure. 



Nervous System. — Caffeine is a certain and direct stimulant to the 

 higher nervous centres (cerebral cortex). 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 animals caffeine often causes the most intense cerebral ex- 

 citement 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 convulsions are of cerebral or spinal origin. The motor and 

 sensory nerves are unaffected by medicinal doses. Caffeine opposes the 

 depressant action of opium and alcohol. It antoginizes alcohol in stimu- 

 lating the highest or controlling functions of the brain, the reasoning 

 faculties, perception of sensory impressions and associations 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 like that seen in rigor mortis. 

 On muscle fibres, removed from the body, it acts in the same way by 

 coagulating the muscle proteids. In small quantities in the body it 

 stimulates the muscle to contract and increases its capacity (10-30%), 

 and endurance 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 chiefly to be attributed to its 

 effect on the muscles themselves. 



Kidneys. — Caffeine often increases the blood supply and volume of 

 the kidneys, as shown by Roy's oncometer. But diuresis occurs in the 

 isolated kidney, and without rise in general blood pressure. Also when 

 the kidney is enclosed in plaster-of-paris so that it can not expand. 

 Therefore diuresis is not due to circulatory changes. The renal cells 

 must be stimulated, and perhaps resorption in the tubules is lessened, 

 since, under caffeine, the composition of the urine is more like that of the 

 blood (increased chlorides). The drug is therefore a local diuretic and 

 (with theobromine) is the most efficient and powerful. No other drug 

 can produce such a flow of urine. 



Respiration. — The respiratory centres (and muscles) are stimulated 

 (along with the vagus and vasomotor) by caffeine in moderate doses, and 

 depressed by toxic amounts. 



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