4 PRELIMINARY CONSIDERATIONS 



which tends to delay absorption and lessen the action of 

 medicines given by the mouth. 



If drugs are irritating they should be given to animals 

 on the food, or after feeding, in order that they be sufficiently 

 diluted. Some remedies require hydrochloric acid for their 

 solution — as iron — and they should therefore be adminis- 

 tered at or after the time of feeding, because hydrochloric 

 acid secretion is then active. 



Elimination of Drugs. 



A drug is as much outside the body when within the 

 digestive tube — so far as any action it may have on the body 

 (unless an irritant) — as if it were on the skin. When ab- 

 sorbed, a medicine passes into the blood vessels or lymphat- 

 ics and thence into the general circulation. That portion 

 which enters the portal circulation reaches the liver and 

 may be destroyed in part (some alkaloids) by this organ. 

 After entering the blood the drug is thought to form 

 unknown combinations with the tissues for which it 

 has an affinity — thereby exerting its remedial effect — and 

 is decomposed or rarely accumulates in the body, but usually 

 is eliminated either unchanged or as decomposition-pro- 

 ducts in the breath, or by the excretions or secretions of the 

 kidneys, bowels, liver, sudoriparous, salivary and mam- 

 mary glands, and mucous membranes. The urine is the 

 most frequent channel of elimination for soluble drugs. 

 The bowels constitute the next more common pathway of 

 elimination. Volatile drugs (chloroform, ether) are elimin- 

 ated very rapidly, usually in the breath. If a drug is 

 eliminated slowly the duration of its action is correspondingly 

 long, and vice versa. This fact will guide us in the frequency 

 of administration of medicines, since if a drug which is 

 tardily eliminated be given at frequent intervals it may be 

 absorbed faster than it is excreted and so accumulate in the 

 body and cause poisoning. The so-called Cumulative Action 

 of a drug refers to the occurrence of a sudden and violent 

 effect during its medicinal administration. This may be due. 



