= Solution
\b[The assertion is too absolute: a remedy can cause a distant response through a <reflex> or another intervening physiological change without first being absorbed into the <blood>.] It is substantially right for the direct action of a circulating <drug> on a distant target, but does not describe every remote effect of treatment.
Three mechanisms should be distinguished:
* \b[Direct action after <drug absorption>.] An orally administered <drug> that acts directly in the <brain> must gain access to that tissue. Absorption from the <gastrointestinal tract>, transport in the <blood>, and passage to the target explain such a systemic action. Changing the route changes the first step: a subcutaneous medicine must leave its local depot, whereas an intravenous medicine is introduced directly into the circulation. The literal word “absorbed” is consequently too restrictive even before considering <reflexes>.
* \b[Local action followed by a neural response.] Stimulation of <sensory nerves> at one surface can cause a response elsewhere through the <nervous system>. Gastric stimulation can evoke <vomiting>, including coordinated movement of respiratory and abdominal <muscles>; sensory input from the <gastrointestinal tract> reaches brainstem circuits through <vagal afferents>. No requirement follows that the original gastric irritant must itself circulate to every contracting <muscle>. A swallowed emetic can have more than one mechanism, however: an observed instance of <vomiting> alone does not prove that absorption played no part.<Nausea and Vomiting Related to Cancer Treatment by the National Cancer Institute>[“Pathophysiology of N&V”; visceral afferent inputs and output to abdominal musculature and respiratory centres]{ref}
* \b[Local action followed by a change in the body's contents.] As a present-day illustration, an osmotic <laxative> can retain <water> in the intestinal lumen and promote evacuation with limited systemic absorption. Any secondary change in fluid balance or symptoms is then a consequence of the local intestinal action, not proof that the laxative has directly acted on a remote organ. The <polyethylene glycol 3350> information from MedlinePlus describes retention of <water> in stool; the regulatory monograph records minimal absorption.<Polyethylene Glycol 3350 by MedlinePlus>[“Why is this medication prescribed?”; retention of water in stool]{ref}<PegLyte prescribing information>[“Action and clinical pharmacology”, p. 9; mechanism and pharmacokinetics of PEG 3350]{ref}
The distinction is between transport of the medicinal substance and transmission of its consequences. A <reflex> transmits activity in <neurons>; a locally acting intestinal agent changes a physical condition; a circulating <drug> delivers molecules to its distant target. The same remedy may combine these routes, and an apparently rapid effect does not by itself settle which route caused it.
A useful experimental design would therefore compare remote responses with measurements of the agent in <blood>, and would test the proposed neural pathway separately. In an appropriate physiological preparation, recording the response while interrupting a relevant afferent pathway can test whether that pathway is necessary; preserving the circulation while interrupting nerve conduction distinguishes neural transmission from vascular transport. Conversely, a remote effect after vascular transfer supports a circulating agent, provided contamination and other transferred mediators are controlled. Failure to detect a <drug> is only as strong as the analytical detection limit.
\b[Absorption is one route to remote action, not a universal prerequisite for every distant physiological consequence.] The historical language “animal economy” means the functioning organism; it should not conceal the distinction between a direct <pharmacological effect> and a secondary <physiological response>.
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