Experiments are reported which show that in all probability the increased resistance to tuberculous infection which is imparted to mice by the removal of the spleen is a consequence of the loss of a function of the organ. This function can be restored by the feeding of fresh spleen. For the present we attribute these changes to the removal and restoration, as the case may be, of a particular substance for which the designation tuberculosplenatin is suggested. This substance is assumed to be related to the spleen as adrenalin is related to the adrenal gland. It is peculiar to the organ but not to the species. It is not found in other organs of the body so far as our observations have extended. The absence of the substance from the lymphatic glands seems of especial importance in this connection.

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