Mother mice which have recovered from an infection with Tryp. duttoni transmit to their young protective substances which render the young resistant to infection with this parasite. The young animals acquire their resistance principally after birth through the ingestion of milk from the immune mother. The young born of a normal mother promptly acquire resistance against Tryp. duttoni if permitted to nurse the specifically immune mother.

The immune substances are secreted by the mother not only in the colostrum, but also in the milk later passed, and nurslings until 15 days old as well as those newly born can absorb the protective substances from the intestine after ingesting the milk of the immune mother. Accordingly, it is possible for a mother who has been infected after the birth of her litter to develop and transmit protective substances to her nurslings in sufficient amount to protect them measurably against a subsequent infection.

A mother mouse passively immunized by the injection of serum from a mouse which has recovered from Tryp. duttoni is also able to transmit protective substances to the young which nurse her.

The immunity of the young mice is specific, and nurslings injected with Tryp. cruzi will become infected even though they nurse a mother immune to Tryp. duttoni.

It is pointed out, in discussion, that the mouse differs as to the principal route of transfer of the protective substances to the young from that generally accepted for hemochorial mammals.

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