Experiments described in a previous report (1) indicated that the serum of rats infected with C. crassicollis contained two types of functional antibodies. The first type, detectable within one week both in infected and in artificially immunized animals, brought about the destruction of larvae before encystment and was referred to as “early” immunity. The second type, detectable only after several weeks of infection, and not at all in artificially immunized animals, was responsible for a marked increase in the destruction of larvae after encystment and was referred to as “late” immunity. Since the nonabsorbable protective property, as well as the late immunity reaction, was found (2) to appear only in infected animals several weeks after infection, some relationship between these two reactions was suggested. Under the previously prescribed experimental conditions no measure of the late immunity was obtainable because the methods which were used, produced complete early immunity, i.e., no parasites were present.

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