Epidemiology often affords unique instances of immunity to disease that call for careful inquiry to explain them. The freedom of certain areas from invasion by infections which have devastated neighboring regions is frequently a phenomenon that, when understood, will reveal secrets of importance in respect to the implantation of disease. An instance of what is here referred to is found in certain parts of India. Although much of that country has suffered severely from the plague, the Madras Presidency has been affected to a relatively slight degree. To account for this immunity has been one of the many problems confronting the British commission appointed to deal with the plague in India. The ninth report,1 just issued by the advisory committee appointed by the secretary of state for India, the Royal Society of London and the Lister Institute, deals with this subject.
As a starting point it must be emphasized