10 CIECUMSTANCES MODIFYING THE ACTION OP DRUGS 



tention of enemata is facilitated by pressure on the auas 

 with a towel for some minutes after the injection is given. 



Solids are sometimes employed by rectum in supposi- 

 tories. For general uses of enemata, see p. 30. 



7. Drugs are absorbed very slightly by the skin, and then 

 ■only when rubbed very vigorously into the epidermis- (in- 

 unction) with lanolin, fat or oil of some kind. Mercury, 

 silver and iodine are most commonly employed for absorp- 

 tion, but drugs are usually applied externally for their local 

 action only and not to influence the general system through 

 i}he blood. 



Dosage. 



The study of dosage is known as Posology. The action 

 of drugs is altered both in degree and in kind by the dose. 

 Thus, increasing the dose would naturally lead to an in- 

 'crease in the intensity of a drug's action, but it frequently 

 ichanges the entire character of the action as well. 



Drugs, as strychnine, acting especially on the ner- 

 vous system, often excite in therapeutic doses, but de- 

 press and paralyze in toxic doses. Drugs, as digitalis, 

 stimulating the heart in medicinal doses, usually depress 

 and paralyze the organ in poisonous doses. Many drugs 

 promoting urinary secretion, in ordinary doses, cause inflam- 

 mation and urinary suppression in large doses. The best 

 way to determine the dose of a drug is to estimate the- 

 amount required for each pound of live weight. This only 

 applies to the same species and to animals of ordinary 

 build. Fat is a comparatively inert tissue as far as the 

 action of drugs is concerned, so that a very fat horse, 

 weighing, for example, 1,200 pounds, would be affected 

 in a more pronounced manner by a dose of medicine 

 than would a lean horse of the same weight and taking 

 the same dose. In the case of young animals, and of 

 those either above or under the ordinary size of the 

 adult of any species, the dose should be proportioned — ac- 

 cording to weight — to the average dos6 for the adult animal 

 of that species. Thus, if the average weight of a horse is 

 1,000 pounds, the dose of any drug for a colt weighing 



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