Mice so x-rayed as greatly to reduce the lymphoid tissue are rendered highly susceptible to tuberculous infection. On the other hand) when a marked lymphocytosis is induced by first immunizing mice against, and then inoculating them with cancer, the resistance to tuberculous infection is greatly enhanced. This heightened resistance may be set aside and even changed to a state of increased susceptibility to the infection by again depleting the lymphocytes by means of the x-ray.

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