‘In the now extensive literature relating to the malaria treatment of general paralysis, the statement is not infrequently encountered that maintenance in the human host for prolonged periods, by direct inoculation of infective blood from one individual to another, modifies the malaria parasite in certain important respects.

...

In previous papers (Yorke and Macfie, 1924, and Yorke, 1925) reference is made to the fact that a strain of Plasmodium vivax maintained by direct passage in the human host since September, 1922 -partly at Whittingham, and partly at Sheffield, mental hospitals - was still capable of infecting A. maculipennis at various passages up to the forty-first.’ (327)