We have previously referred to the fact that a certain number of Bombay rats were immune both to subcutaneous and to cutaneous inoculations of virulent plague bacilli. In paper V, p. 505 above, we were able to record that 59% of rats in Bombay could withstand the rubbing on scarified surfaces of emulsions of spleens of rats which had died of acute plague. The fact that a large number of rats in India, where plague had occurred, were more or less immune has been noted by Simond and Walton.