128 STIMULANTS TO CENTRAL NERVOUS SYSTEM 



movements and excitement. The medullary centers are excited, 

 causing a stimulation of the respirations and a general vasoconstric- 

 tion. The cardio-inhibitory center is probably also stimulated, but 

 this is of but little importance because the peripheral action of caf- 

 feine on cardiac muscle so overshadows its action on the center. The 

 action upon the cord and medulla is quite similar to that of strychnine 

 but weaker. There is the same increased reflex excitability fol- 

 lowed by tremors and tetanus but this action follows only large doses. 



Muscles. Caffeine increases the contractility of all forms of 

 muscle. Small doses increase the contractility, strength and power 

 for work of all muscles. After large doses the muscles Jbecome ex- 

 hausted, hard, and pass into a rigor that closely resembles rigor 

 mortis. 



Kidneys. Caffeine is a decided diuretic. The water of the 

 urine is increased to a greater extent than the solids, so that it is low 

 in specific gravity, yet the total amount of solids eliminated is not 

 diminished. It is generally believed that caffeine and its allies 

 stimulate the tubules of the kidneys to an increased action and that 

 its diuretic action is independent of the circulation. But there is 

 another theory that caffeine dilates the vessels of the kidneys and 

 produces diuresis in this manner. Whether the dilatation of the 

 vessels is the cause of the increased secretion or the result of kidney 

 activity cannot be definitely stated. At any rate caffeine and its 

 allies act in a specific manner on the kidneys and do not cause irri- 

 tation. 



Metabolism. Caffeine is believed to increase metabolism. It 

 raises temperature slightly, due no doubt to stimulation of the central 

 nervous system and on account of increased movements. 



Absorption and Elimination. Caffeine is rapidly absorbed 

 and is chiefly eliminated by the kidneys. Some of the drug is ex- 

 creted unchanged, some is changed into other compounds, but the 

 fate of the greater part is unknown. 



Therapeutics. Caffeine is not an important remedy in veter- 

 inary medicine. It may be used as a cardiac stimulwnt and tonic 

 although it is not so efficient in valvular insufficiency as digitalis. 

 When marked dropsy is present a combination of digitalis and 

 caffeine may be of more service than either alone. 



Diuretic. Since caffeine is a nonirritating diuretic it may be 

 used in nephritis. 



Narcotic Poisoning. Caffeine is often serviceable in cases of 

 narcotic poisoning on account of its stimulating action on the heart, 

 respirations and brain. Strong coffee may be used in emergency. 



