Opposition
in astronomy, the situation of two heavenly bodies when they are diametrically opposed to each other, or when their longitudes differ by 180°.
Thus there is always an opposition of sun and moon at every full moon; also the moon, or a planet, is said to be in opposition to the sun when it passes the meridian at midnight. In logic, opposition of judgments is the relation between any two which have the same matter, but a different form, the same subject and predicate, but a different quantity, quality or relation. There are five kinds of opposition, viz., contradictory, contrary, inconsistent, subaltern, and subcontrary. In rhetoric, a figure whereby two things are joined which seem incompatible. a OPSONIN. A substance which is believed to exist in the blood, and whose function it is to stimulate the phagocites in their attack upon harmful bacteria, possibly by rendering these foreign micro-organisms more readily absorbable.
The opsonic index is the ratio between the power of absorbing bacteria possessed by the blood under healthy conditions and that possessed under pathological conditions. In other words, the higher the opsonic index, the greater is the resistance of the body to disease. It has been found that the opsonic index can in certain diseases be raised by injecting into the blood dead bacteria of the species producing the disease.