During the middle ages cattle and sheep were the chief farm animals, but the intermixture of stock consequent on the common-field system was a barrier to improvement in the breed and conduced to the propagation of disease.
They are effected chiefly by some alteration in the description of the root-crop, and perhaps by the introduction of the potato crop; by growing a different cereal, or it may be more than one cereal consecutively; by the growth of some other leguminous crop than clover, since " clover-sickness " may result if that crop is grown at too short intervals, or the intermixture of grass seeds with the clover, and perhaps by the extension by one or more years of the period allotted to this member of the rotation.
Yellow Soap consists of a mixture of any hard fatty soap with a variable proportion - up to 40% or more - of resin soap. That substance by itself has a tenacious gluey consistence, and its intermixture in excess renders the resulting compound soft and greasy.
The native carbonate or cerussite (q.v.) occasionally occurs in the pure form, but more frequently in a state of intimate intermixture with clay ("lead earth," Bleierde), limestone, iron oxides, &c. (as in the ores of Nevada and Colorado), and some times also with coal ("black lead ore").
The unrestricted intermixture of these three races forms the principal basis of the Brazilian population at the beginning of the 10th century.