morbific

New Crobuzon was a huge plague pit, a morbific city.

She could have taken herself off to the local Italian with her child and a book of her own, for Kate also likes reading though her tastes are less morbific.

Zhirek, a world of time before, had searched a valley for slicing stones, had drunk from the morbific water of it, had sought to hang himself on its tree and to throw himself down from its overleaning height.

The fermentation theory of disease is the (now obsolete) concept that many diseases, including the diseases which were "epidemic, endemic and contagious", owe their origin to the presence of a "morbific principle" in the system, acting in a manner analogous to, although not identical with, the process of fermentation.