"On the [contingent] contagion of cholera"
(29 October 1831): 3,f
PDF courtesy of the Times Digital Archive, Michigan State University Libraries.
One extract that shows Johnson believed cholera was normally non-contagious, contingently contagious in very rare circumstances:
"That a focus of infection may be generated occasionally in deep cellars, and the crowded hovels of poverty, I do not doubt. The same takes place every year with fevers and other diseases. But that the germs of cholera can be thence carried by individuals in health throughout this country, I will not believe, because it is contrary to experience."
Another repeats Johnson's deeply erroneous prediction:
"I have no hesitation in reiterating my opinion that if cholera come to these shores, it will be shorn of its fatality, and coercible to a degree that will make the terrorists [those who predict the opposite and, in Johnson's opinion, needlessly incite fear in the populace] ashamed of their ominous predictions and their visionary speculations."