A quiet day with northerly wind; the temperature rose gradually to zero. Having the night duty, did not go out. The moon has gone and there is little to attract one out of doors.
Atkinson gave us an interesting little discourse on parasitology, with a brief account of the life history of some ecto- and some endo-parasites – Nematodes, Trematodes. He pointed out how that in nearly every case there was a secondary host, how in some cases disease was caused, and in others the presence of the parasite was even helpful. He acknowledged the small progress that had been made in this study. He mentioned ankylostomiasis, blood-sucking worms, Bilhartsia (Trematode) attacking bladder (Egypt), Filaria (round tapeworm), Guinea worm, Trichina (pork), and others, pointing to disease caused.
From worms he went to Protozoa-Trypanosomes, sleeping sickness, host tsetse-fly – showed life history comparatively, propagated in secondary host or encysting in primary host – similarly malarial germs spread by Anopheles mosquitoes – all very interesting.
In the discussion following Wilson gave some account of the grouse disease worm, and especially of the interest in finding free living species almost identical; also part of the life of disease worm is free living. Here we approached a point pressed by Nelson concerning the degeneration consequent on adoption of the parasitic habit. All parasites seem to have descended from free living beasts. One asks ‘what is degeneration?’ without receiving a very satisfactory answer. After all, such terms must be empirical.