Final answer:
A parasympatholytic drug inhibits the parasympathetic nervous system, leading to effects like pupil dilation, known as mydriasis.
Step-by-step explanation:
A parasympatholytic drug inhibits the parasympathetic nervous system's activity. The parasympathetic nervous system is involved in the 'rest and digest' responses of the body, opposing the sympathetic system's 'fight or flight' responses. Since parasympatholytic drugs decrease parasympathetic activity, they result in effects similar to sympathetic stimulation.
The correct answer to the question of which effect a parasympatholytic drug would have on an animal is B. Mydriasis, which is the dilation of the pupil. This occurs because parasympatholytic drugs inhibit the action of the parasympathetic nervous system on the eye's muscles, which normally constrict the pupil. As a result, the opposing sympathetic influence, which causes dilation, goes unopposed.