A final important test in identification is that of pathogenicity. Nowak induced abortion in pregnant guinea pigs with great regularity by subcutaneous, intraperitoneal, and intravenous injection of pure cultures of the abortion bacillus. So far, four pregnant guinea pigs have been inoculated subcutaneously with the pure cultures isolated by us, and the inoculation has been followed by premature evacuation of the uterus with death of the fetuses in 3-½ 8, 6, and 7 days respectively. In the first guinea pig the two fetuses were practically fully developed and covered with hair. In this instance the abortion bacillus was isolated only from the subcutaneous tissue of the mother at the point of inoculation, the cultures from the uterus, the placenta, and the fetuses remaining negative. In the other three cases the fetuses were undeveloped and the condition was that of a true abortion. In these instances the abortion bacillus was demonstrated by culture tests at the point of inoculation in pure culture in two, in mixed culture in the other one; in the interior of the uterus in pure culture in all three; in each of the four placentæ of two cases in mixed culture, as these placentæ had been passed some time before they were found, and in the three placentæ of the other case in pure culture; in the livers of all three fetuses of the one case in pure culture, but not in the other four fetuses; in the heart blood of the mother in pure culture in one case, but not in the other two cases. In all these tests the mother guinea pig was killed by chloroform soon after the abortion had occurred. From the results of these tests we have concluded that the bacillus isolated by us from aborting cows is identical with that isolated by Bang and by Nowak. Further, the investigations of Bang, Preisz, Nowak, McFadyean and Stockman, and Zwick, seem to justify the acceptance of this organism as the infectious agent in the contagious abortion of cattle.