Although much work on the epidemiology of plague has been done in many parts of the world since the discovery of the Bacillus pestis in 1894, the origin of the outbreaks in Eastern and Southern Russia has, until a short time ago, remained obscure. Transbaikalia, together with extensive areas of Northern Manchuria and North-east Mongolia that are conterminous with it, and, again, the region in Southern Russia which includes the Kirghese and Kalmuck steppes and especially that portion of it which lies between the lower reaches of the rivers Volga and Ural have long been known to contain endemic foci of plague, and have been the source of considerable outbreaks of pneumonic plague. Thus, in the winter of 1878–79, an outbreak of this type at Vetlianka, a Cossack village on the right bank of the Volga, caused alarm in Western Europe. Competent epidemiologists–British, French and German–visited the village after the event, and examined the circumstances that favoured the spread of the infection. Their observations were brought together and analysed by Netten Radcliffe (1881) in his memorandum on plague, which gives the first adequate description of a pneumonic plague epidemic. The more recent epidemics of pneumonic plague, namely, those of Manchuria in 1910–11 with 50,000 deaths, Middle China in 1917–18 with 15,000 deaths, and Manchuria in 1920–21 with 9000 deaths, owed their origin to ill-defined centres of infection in the immense tract of land which includes Transbaikalia and which is contiguous to the north-west boundary of China.