CAFFEINE 375 



Nervous System. — Caffeine is a certain and direct stimu- 

 lant to the cerebral cortex. It produces wakefulness and 

 restlessness, and stimulates the reasoning and imaginative 

 faculties in man. In the lower animals caffeine often causes 

 the most intense cerebral excitement and mania in large 

 doses. The alkaloid also stimulates the spinal motor area, 

 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. Alcohol and opium stimulate the brain, 

 but do so incoordinately. This is net the case with caffeine. 



Kidneys. — The kidneys primarily contract for two or 

 three minutes with coiresponding diminution in the flow of 

 urine, after the subcutaneous injection of small doses of 

 caffeine. This effect is independent of the general vascular 

 condition, and is followed by an increase in the volume of 

 the kidneys, with accompanying augmentation of the urinary 

 secretion, as shown by experiments with Roy's oncometer. 

 The renal cells are directly stimulated. The drug is there- 

 / fore a local diuretic and one of the most efficient and 

 powerful. 



Respiration. — The respiration is not affected to any 

 considerable extent by caffeine, save by toxic doses, when 

 it is depressed. 



Metabolism. — The action of caffeine (and coffee) upon 

 tissue change is inconstant. Sometimes it restrains nitro- 

 genous consumption with corresponding diminution of urea 

 elimination. Caffeine is entirely decomposed in the body, 

 unless ingested in large quantities, when it is eliminated in 

 part in the urine. 



Toxicology. — Caffeine is a spinal and muscle poison to 

 the frog. Tetanic convulsions occur in the batrachian 

 similar to those produced by strychnine, but there is also 

 muscular rigidity. These phenomena follow the direct 

 stimulation of the spinal motor tract and muscles, and are 

 succeeded by paresis. In man, stimulation of the cerebral 



