ACTION OF SALICYLIC ACID 361 



are powerful antiseptics resembling carbolic acid in action but less toxic 

 and irritant. A solution of salicylic acid (1-60) is equivalent to a solu- 

 tion of carbolic acid (1-22) in destroying some bacteria, but is not gen- 

 erally as useful, being less penetrating in its action on the tissues. In 

 solution salicylic acid softens and removes the horny layer of the skin 

 without causing any soreness. Salidylic acid, sodium salicylate and sali- 

 cin, in their pure state, are irritating to the unbroken skin or raw surfaces. 

 Salol is not. 



Action Internal. — Salicylic acid is an irritant in the digestive tract 

 and in large doses causes nausea and vomiting in dogs. It slightly in- 

 creases the flow of bile. Salicylic acid is converted into salicylates by the 

 alkaline intestinal juices, and is absorbed in this form, chiefly as sodium 

 salicylate. For this reason, and because the latter salt is less irritating 

 than salicylic acid, sodium salicylate is preferred to the acid when a con- 

 stitutional action is desired. Salicin splits up in the bowels into salicylic 

 acid, salicylous acid (HC7H5O2), salicyluric acid (HCgHgNOJ, and 

 glucose. Salol is decomposed by the pancreatic juice into salicylic acid 

 (64 per cent.) and carbolic acid (36 per cent.). After large doses the 

 urine takes on the characteristic smoky color produced in poisoning by 

 phenol. Salol is an intestinal antiseptic. Salicylates retard enzyme 

 action. 



Circulation. — Moderate doses of sodium salicylate, or salicylic acid 

 slightly increase blood pressure by stimulation of the heart muscle and 

 vaso-constrictor centre, but large doses depress the heart force, blood 

 pressure and nervous system. The artificial acid is said to be more 

 depressant than natural salicylic acid obtained from plants, because of 

 orthocreosotic and metacreosotic acids existing as impurities in the former. 

 Natural salicylates cost 5 to 10 times as much as the artificial, and Eggle- 

 ston, from an exhaustive recent study, states that there is no material 

 difference in the action of the two. 



Nervous System. — The only known action of salicylic acid on the 

 central nervous system is that on the medullary, respiratory and vaso- 

 motor centres which are first stimulated, then depressed, and finally 

 paralyzed by lethal doses. v 



Therapeutic -quantities often cause, in man (salicylism), ringing in 

 the ears and headache. Besides, some deafness, dimness of vision and 

 excessive perspiration are not uncommon after large doses. 



Respiration. — The respiratory movements are primarily quickened by 

 the stimulation of the peripheral vagi and respiratory centres produced 

 by sodium salicylate and salicylic acid; but after large doses the respira- 

 tory centres are depressed and paralyzed and death takes place by 

 asphyxia. 



Temperature. — Medicinal doses do not influence the normal tempera- 

 ture of healthy animals, but do often lower bodily heat in fever, and fre- 

 quently induce sweating. The largest therapeutic doses must be given 

 to secure an antipyretic action. Antipyresis occurs from heat loss due 

 to dilation of cutaneous blood vessels. 



Kidneys and Elimination. — Salicylic acid, salicin and sodium salicy- 



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