‘Discussion. - Sir Rickard Christophers: Of the various points dealt with by the authors of the paper, that relating to the effects of "dose" of infection is one of the most important... From experience of the conditions under which such infections are acquired it is much more probable that the severity of the case has been brought about by massive inoculation of sporozoites. In the laboratory it certainly appears that in bird-malaria infections may be "worked up" by choosing heavy gametocyte carriers for infecting the mosquitoes, just as has been described in human malaria by the authors of the paper at Horton. Recently, in order to obtain uniformity in series of infected birds used in carrying out certain drug tests, it was thought that it might be a good thing for each bird to be bitten by a single mosquito known to have sporozoites in the glands. The plan, however, did not work, owing to the number of negative cases following such a procedure, even though in every case it was certain that the bird had been fed on and that the mosquito feeding had sporozoites. A number of these birds, however, developed infection eventually, say by the tenth or twelfth day instead of on the sixth day. It seemed probable that here minimal dosage had delayed the appearance of infection.

In regard to the causation of epidemics, the final and fully satisfactory answer can onlybe arrived at when the actual conditions have been worked out in the field... [893-894] if we suppose that in normal years time allows only for three geometrically increasing cycles, merely an ordinary fever season results. Increase in the period of optimal conditions (humidity, temperature, &c.), antedating by four weeks the normal, might well, by allowing for a further cycle with its magnified effect, make this an epidemic year.’ (893-894)