He was interested in a disease called bacillary dysentery, which is a bacterial infection that causes severe diarrhea, and back then, was actually killing a lot of people, because after all, no cure for bacterial infections had been invented.
Na altura, ele estudava a doença disenteria bacilar, uma infecção bacteriana que provoca casos graves de diarreia, o que na época levava à morte  de bastantes pessoas, pois ainda não existia uma cura para infecções bacterianas.