the Therapeutic Immunity Reaction in the Differentiation of Trypanosome Species

When mice infected with the parasites of caderas, dourine, nagana, surra of India, or surra of Mauritius are properly treated with various therapeutic agents, a temporary immunity is produced. As the immunity is specific (I), the hope was at one time entertained that the reaction might be of service in differentiating trypanosome species. This expectation, however, almost vanished when the delicacy of the reaction began to be appreciated. By means of it, Ehrlich2 (2) and Browning (3), and subsequently the writer (4), were able to distinguish strains of trypanosomes known to have had a common origin, but rendered resistant to various medicaments. With equal clearness the reaction enabled the writer to differentiate normal trypanosomes supposed to have had a common origin, i. e., the organisms of surra of India and surra of Mauritius. Although this extreme delicacy apparently rendered the reaction useless in determining species, objections could be raised to drawing this conclusion from the evidence cited. First, the resistant strains differentiated were no longer normal. As they had acquired new characteristics it seemed scarcely permissible to draw from them inferences as to the behavior of organisms that had never come in contact with therapeutic agents. Second, the common origin of surra of Mauritius and surra of India is still questioned, although the majority of the authorities seem to be of the opinion that the Isle of Mauritius became infected through thle importation of