1. “It has often happened that hundreds of men in a camp have been seized with the dysentery, almost at the same time, after one shower of rain, &c. People under similar circumstances must be subject to similar diseases: and yet it often happens that dysentery begins with a few people, and spreads itself by degrees until a multitude are affected.” This argument rather militates against himself; for, if dysentery or any other disease was occasioned by an _evident_ general cause operating upon persons in similar circumstances, all of them ought to be taken ill at once; but Dr. Mosely owns that they frequently are not. There must, of consequence, be something _less evident_ which determines the disease to particular persons, while the general cause operates equally upon all. This less evident cause we call _contagion_. 2. “It is incredible that the smelling a little human blood, that had stood some months in a phial, gave the man a dysentery mentioned by Pringle; or that the person Forestus speaks of got the plague by only putting his hand into an old trunk; or that the shaking an old feather-bed, which had lain by seven years, raised a plague at _Wratislau_, which destroyed five thousand persons in twelve weeks, as related by Alexander Benedictus, &c.--Such things _may be true_, but, when probability is shaken, reason always inclines to skepticism.” Here our author most evidently contradicts himself; for in the beginning of the paragraph he tells us that the things related are _incredible_, and in the end of it, that they _may be true_. The argument, if it may be so called, is mere assertion. It is _incredible_ that the smell of putrid human blood in a vial should produce the dysentery. Why should this be more incredible than that smelling to a charged vial should ensure an electric shock to the person who did so? This is entirely a question respecting a matter of fact, not of speculation. The same is the case with the rest. It is not more incredible that, if the infection of the plague was in a trunk, a man should get the plague by putting his hand in it, than that he should be burnt if he put his hand into a trunk full of hot ashes. Before the Doctor decided in such a positive manner, he ought to have proved that no infection could be contained in a trunk; but this, though the very point in question, he takes for granted, first telling us that the contrary is incredible, and then that it may be true!