As long as the sib advisers exercised an unweakened control a certain number of questionable marriages could be handled in such a decisive way as to make them out of the question. Among these was the repudiation of any marriage with sibs in which an incurable blood disease was present, such as elephantiasis, exostosis, herpes. The consequence was that families afflicted in this way could marry only among themselves. That relatively so small a percentage of elephantiasis is found in the poulation is to be explained in this way. A sickness called "kifuwa" was also a disqualification for marriage and this, according to all descriptions, was tuberculosis. It is possible that the disregard of the old sib rule has contributed to the deplorable increase of this disease among the Chagga.

The probable direction taken by fate in a sib was also important in the eyes of those who had the guardianship of marriage. They warned against marriage into a violent sib which increased its possessions through open or secret evil deeds. Such marriage would involve the ultimate fate of extinction through the vengeance of ancestors.

Marriages into sibs where magic was known or thought to be practiced were also discouraged. This evil would inevitably be transplanted to one’s own sib. They said, "A sorcerer’s daughter splits the house."

They adhered most emphatically to the principle that no sib son should bring home a daughter from a thieving or lazy sib. The saying, "They teach their children laziness" was enough to terminate an engagement. And a good sib would not allow a daughter to marry into a lazy household.

But not all industrious girls were recommended for marriage. It must be known whether they were ngula, gormandizers, who would store no foods and hardly wait until they were ripe. Whether a girl would become a mngula was recognized from her mother. If the mother was a mngula the daughter was sure to be one.

Only the old sib advisers could determine the choice of a bride to the advantage and continuity of the sib, and since irresistible modern factors have unconsciously undermined to a large degree their influence marriage is left more and more to the individual pairing instinct which is concerned almost exclusively with externals and contributes in only a secondary way to the maintenance of the health and particularly the moral qualities of the race (75–76).

It seems probable that this extraordinary interest of a primitive people in practical eugenics is related to their peculiar interest in the preservation of the original ancestral line.

It is noticeable that in their attention to blood the Chagga do not employ freely the device of blood brotherhood. The symbolism of life unity through exchange of blood which is widely employed in Africa is most frequently a pact between individuals made, for example, by sucking blood from a cut in the arm of each by the other. The blood bond may thus unite total strangers, serving as an impressive and magical form of introduction and life insurance.

This practice is secretly employed among the Chagga as a union of the life interests of two individuals, but the dominant concept relating to blood is not that of a bond between individuals but of a continuous blood bond between generations. A blood bond with a stranger is thus a misuse of blood.

Among the Chagga at present this blood symbolism has taken two main directions—blood bonds between two sibs with a view to self-protection and aggrandizement against other sibs, and blood bonds between separate tribes and chiefs. (The ceremonies in this connection are described in Chap. VI.)