It is highly satisfactory to find that the character of this mouse-bacillus has stood the test of time, for after a period of more than ten years most encouraging reports concerning its efficiency still continue to be received. In one of the latest of these, drawn up by the Director of the Experimental Agricultural Institute in Vienna, we read that in no less than seventy per cent. of the cases in which it was employed it was completely successful in its work of extermination, and it is interesting to note that in a considerable number of these instances it was the domestic mouse against which its energies were directed. The rat has, however, until recently escaped the hand of the bacterial executioner, but his knell has also now been sounded in the announcement that a rat-bacillus has been discovered. Considering the undesirable notoriety which these rodents have of late obtained in connection with their undoubted culpability in the dissemination of plague, this discovery, if correct, should be warmly welcomed. That there is plenty of work awaiting such a micro-organism may be gathered from the fact that during the outbreak of plague in Sydney the crusade against rats which followed led to the slaughter in one year of over 100,000. The discoverer of this useful member of the microbial community is Tssatschenko, of the University of St. Petersburg, and in his memoir he states that, whilst highly virulent as regards rats, it is quite harmless to domestic animals of various kinds. Thus cats, dogs, fowls, and pigeons when fed with food infected with the bacillus suffered no ill effects whatever, whilst its administration in large quantities to farm stock, such as horses, oxen, pigs, sheep, geese, and ducks, was also without result; hence its distribution, according to its discoverer, offers no danger to other animals.