(From eligo,to choose, or select). This term has been usually applied to chemical affinities; but as we have employed it in physiological discussions, we shall state the foundation on which we rest.
This power is chiefly observed in the absorbent system. There is little doubt but that, on the surface, noxious vapours and noxious fluids are not taken up; and, apparently, when watery fluids are not wanted, even water is not absorbed. In many cases, when the introduction of medicines into the circulating system was thought necessary, numerous experiments were made to discover whether the chyle was impregnated with remedies given to dogs. These, though sought for at different periods, after having been taken, were seldom found. Thus we have an additional proof of the superintending power of nature to guard the constitution against injury; since, as we have had occasion to remark, the most innocuous fluids injected into the blood vessels occasion the most fatal symptoms.
How far this choice prevails we are not informed. In Dr. Alexander's experiments, bark and nitre seem to have been conveyed to the blood, as they appeared in the urine. Even at the first view, these experiments appear inconclusive,and other more accurate observers have not supported his opinion.
This elective power appears equally striking in the stomach and intestines. Food the most strange and singular is sometimes longed for. particularly in fevers, about, or after, their crisis; and the desire may be indulged with little injury. The mildest foods are often, by an apparently similar caprice, rejected by this organ and the intestines. In the glandular system we perceive a similar election. The fluids pass through the kidneys often in small and inefficient quantities, apparently from the presence of some medicine which they repel; for, if that is disused, the secretion returns. In this case we find all the other symptoms of a noxious matter; the functions are disturbed, the mind agitated, and fever excited. These symptoms are sometimes owing to an excess of stimulus, which, in weak organs, produces irregular action; but more frequently to the repulsion of the fluids, for where there is attraction, repulsion is also found. Why medicines affect a particular gland or injure the stomach, -though inoccuous in the eye, is a subject not connected with the present, and will be spoken of under the article Secretion; and occasionally mentioned as a specific stimulus.