Moreover, as this complication was a marked feature in certain epidemics of plague in India, the hypothesis has been framed by Hirsch that a special variety of plague, pestis indica, still found in India, is that which overran the world in the 14th century.
But numerous cases of nonfatal mild bubonic disease (mild plague or pestis minor) occurred both before and after the epidemic, and according to Tholozan similar cases had been observed nearly every year from 1856 to 1865.8 The next severe epidemic of plague in Irak began in December 1873.
The melancholy incident illustrates several points of interest: (1) the correctness of the bacterial theory of causation, and the identity of the bacillus pestis as the cause; (2) the infectious character of the pneumonic type of disease; (3) its high fatality; (4) the difficulty of diagnosis.
Whether the numerous pestilences recorded in the 7th century were the plague cannot now be said; but it is possible the pestilences in England chronicled by Bede in the years 664, 672, 679 and 683 may have been of this disease, especially as in 690 pestis inguinaria is again recorded in Rome.
The report also considers it proved that the bacillus pestis multiplies in the stomach of a flea and may remain a considerable time within its host.
It is doubtful whether the distinction drawn between pestis minor and pestis major has a real aetiological basis.