14 CIKCUMSTAKCES MODIFYING THE ACTION OF DEUGS 



JJohit. —This ciicumRtaijce does not Lave the same import- 

 ance iu veterinary medicine which it possesses in human 

 practice, since we control drug habits in animals. Animals 

 usually become less susceptible to the action of drugs 

 on their repetition, e.g., opium and cathartics. This rule 

 does not hold iu the case of drugs having a cumulative 

 1 action, nor in the repeated use of irritants on the skin, for 

 then their action is strongly intensified. 



Disease. ^The action of drugs is profoundly influenced 

 by disease. It is only possible to enumerate a few exam- 

 ples. Pain is almost an antidote to opium, and large re- 

 peated doses of the drug, previously innocuous, may, on the 

 sudden cessation of pain, induce poisoning. Opium is also 

 borne in enormous doses in peritonitis. Inflammation ind 

 congestion of the digestive organs hinders the absorption of 

 all medicines. A congested condition of the alimentary 

 canal, and even of the respiratory tract in horses, contra- 

 indicate the use of strong purgatives in these animals, 

 since superpurgation may occur. A high temperature alters 

 the action of many drugs. 



Opium is not so efficient as an analgesic in fevers, while 

 antipyretics will- not lower the temperature in health. 

 Stimulants are not nearly so potent in depressed bodily 

 conditions, and counter-irritants will not produce their 

 characteristic actions on the skin when the circulatory 

 functions are at a low ebb. 



Idiosyncrasy. — Individual susceptibility to drugs is 

 infrequent, but unfortunately cannot be anticipated. The 

 writer has seen simple zinc oxide (free from adulteration or 

 impurities) cause a frenzy of irritation when rubbed on a 

 dog's skin, and a small dose of tartar emetic cause violent 

 vomiting in a cow. Some animals are very susceptible to 

 counter-irritants. Well-bred animals are commonly more 

 responsive to drugs than others. 



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