Reports of Societies
BMJ (Clinical Research Edition)
The author was of opinion that the concurrence of three classes of causes was necessary for the development of every epidemic. These were: (I) general causes, experienced over large portions of the earth's surface at the same time, and usually alluded to as epidemic causes or influences; (2) causes connected with locality; (3) causes connected specially with persons. If the two latter classes were fully developed, intense disease might be excited under the influence of the general causes; while
... neral causes; while if they were less developed, notwithstanding the operation of the general causes, sporadic cases or small groups only might make their appearance, or the inhabitants of certain localities might escape altogether, while those of others in their vicinity, and often mixed up with them, might display a large amount of sickness. Mr. Lawson had investigated the nature of one of the general causes in connection with fever and cholera, and, from its wave-like character and progressive motion, had denominated it a pandemic wave. The waves followed each other every second year, and proceeded from south to north according to a fixed law, so that their position could be indicated on the map for any given date. [See map in Sanitary Report for the Army for i866, p. 3g3, and Epidemiological Transactions, vol. iii, p. 2I6.] Their influence was experienced in England the sixth year after it had been mani. fested at the Cape of Good Hope ; and, as regarded cholera, in a year with an odd number there would always be the crests of three waves between England and the Cape, and in a year with an even number the crests of two only. Ships proceeding from England to the Cape must pass through these waves, and, when circumstances were favourable for the Wanifestation of cholera in them, the disease should be intensified where their geographical position corresponded with that of the wave at the time. The tracks of four ships proceeding from England or Ireland, and one from Gibraltar, to the south, were given, while cholera existed on board ; and these, with the attacks of the disease each day, were shown on charts, together with the estimated position of the waves at the time for each.