Leviticus 19:19

Thou shalt not let thy cattle gender with a diverse kind—This prohibition was probably intended to discourage a practice which seemed to infringe upon the economy which God has established in the animal kingdom.

thou shalt not sow thy field with mingled seed—This also was directed against an idolatrous practice, namely, that of the ancient Zabians, or fire-worshippers, who sowed different seeds, accompanying the act with magical rites and invocations; and commentators have generally thought the design of this and the preceding law was to put an end to the unnatural lusts and foolish superstitions which were prevalent among the heathen. But the reason of the prohibition was probably deeper: for those who have studied the diseases of land and vegetables tell us, that the practice of mingling seeds is injurious both to flowers and to grains. "If the various genera of the natural order Gramineæ, which includes the grains and the grasses, should be sown in the same field, and flower at the same time, so that the pollen of the two flowers mix, a spurious seed will be the consequence, called by the farmers chess. It is always inferior and unlike either of the two grains that produced it, in size, flavor, and nutritious principles. Independently of contributing to disease the soil, they never fail to produce the same in animals and men that feed on them" [WHITLAW].

neither shall a garment mingled of linen and woollen come upon thee—Although this precept, like the other two with which it is associated, was in all probability designed to root out some superstition, it seems to have had a further meaning. The law, it is to be observed, did not prohibit the Israelites wearing many different kinds of cloths together, but only the two specified; and the observations and researches of modern science have proved that "wool, when combined with linen, increases its power of passing off the electricity from the body. In hot climates, it brings on malignant fevers and exhausts the strength; and when passing off from the body, it meets with the heated air, inflames and excoriates like a blister" [WHITLAW]. (See Ezekiel 44:17-18).