ACTION OF DRUGS 63 



horse at 1000 lbs. as 1, and estimating the dose for weights higher 

 and lower than this, but has not proven very practical and aside 

 from varying the dose for large and small animals, is of little prac- 

 tical use. 



2. Age. The age of the animals is of considerable importance, 

 but with the exception of a few drugs, which act more violently on 

 young animals, is largely lost sight of, except as the dose is graded 

 according to size. Weight is of more importance in veterinary 

 dosage than age, because this varies so greatly in different kinds of 

 each species handled. 



3. Sex. In human practice women require less medicine than 

 men, on account of smaller size and greater susceptibility to any in- 

 fluences. In animals we do not see this difference, but irritant 

 cathartics should be avoided during pregnancy on account of the 

 liability to produce abortion. 



4. Temperament — Eace. High strung animals are more sus- 

 ceptible than phlegmatic ones. This is particularly so in case of 

 drugs acting upon the nervous system. The thoroughbred or stand- 

 ard bred animals are much more susceptible than the draft type. 



5. Tolerance^ Habit. This is of little importance to veterina- 

 rians, as their patients are not addicted to drug habits, but we do occa- 

 sionally find a horse which has been fed arsenic in sufficient amounts 

 to become very tolerant to it. 



6. Idiosyncrasy. This means an unusual reaction to a medicine 

 or food. We occasionally find an animal in which ordinary doses of 

 a medicine will produce an unusual reaction, or one in which ex- 

 tremely large doses are necessary to cause the usual reaction. There 

 are also some animals which must not be fed certain foods on account 

 of disagreeable effects due to a peculiar susceptibility to them. 



7. Species. On account of the structural and physiological vari- 

 ations in the different species of animals, the actions of drugs are not 

 the same for all species. For instance, emetics do not usually 

 produce emesis in horses, opitun and its alkaloids cannot be depended 

 upon to produce sedative action in the horse and always produce 

 excitement in the cat family. Dogs are very tolerant to morphine, but 

 very susceptible to strychnine. Purgatives take much longer to act 

 in the herbivora than in the carnivora or omnivora, etc. 



8. Nature of disease. The nature of the disease has considerable 

 influence upon the action of drugs. Eor instance, the usual seda- 

 tives may have little effect in quieting the severe pain of enteritis. 

 Antipyretics reduce temperature in fever, but not when it is normal. 

 In some febrile conditions, especially influenza of horses, the usual 

 purgative dose of aloes is liable to cause superpurgation. 



9. Object of medication. This may be illustrated by several 

 drugs. Quinine is given in much smaller doses as a bitter than as an 

 antipyretic, ipecac and apomorphine in smaller doses as expectorants 



