Rubuta ci gaba ga wannan sakin layi - Daya daga cikin shahararrun gwaje-gwajen da aka yi a cikin yanayi shine 1854 Broad Street cutar kwalara
a birnin Landan, a ƙasar Ingila. A ranar 31 ga Agusta, 1854, wata babbar cutar kwalara ta afkawa Soho. A cikin kwanaki uku masu zuwa, mutane 127 kusa da Broad Street suka mutu. A karshen barkewar cutar mutane 616 suka mutu. Likita John Snow ya gano asalin barkewar cutar a matsayin famfo na ruwa mafi kusa, ta amfani da taswirar mutuwa da rashin lafiya wanda ya nuna tarin lamura a kusa da famfo.