4 PEELIMINAEY CONSIDEEATIOISrS 



of these parts. Absorption from the stomach and bowels of 

 healthy animals is chiefly influenced by the quantity of food 

 in them. When these organs are empty, absorption is 

 rapid ; but when full, it is slow. For this reason absorption 

 is markedly tardy and imperfect in ruminants. In these 

 animals there is a comp?ratively impervious skin-like 

 mucous membrane and lack of vascularity in the first three 

 gastric compartments ; while a large amount of food is 

 always to be found in the first and third stomachs; all of 

 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. 



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 may form unknown com- 

 binations with the tissues for which it has an afiinity — 

 thereby exerting its remedial effect — and is decomposed or 

 rarely accumulates in the body, but usually is eliminated 

 either unchanged or as decomposition-products in the bream, 

 or by the excretions or secretions of the kidneys, bowels, 

 liver, sudoriparous, salivary and mammary 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 eliminated 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 fre- 

 quent intervals it may be absorbed faster than it is excreted 



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