When, however, the great epidemics made their appearance, the medical men appealed to the works of Galen in vain for enlightenment, as these works, having been written several centuries before the time of the plagues, naturally contained no information concerning them.

It was evident, therefore, that on this subject, at least, Galen was not infallible; and it would naturally follow that, one fallible point having been revealed, others would be sought for.

In other words, scepticism in regard to accepted methods would be aroused, and would lead naturally, as such scepticism usually does, to progress.

The devastating effects of these plagues, despite prayers and incantations, would arouse doubt in the minds of many as to the efficacy of superstitious rites and ceremonies in curing diseases.

They had seen thousands and tens of thousands of their fellow-beings swept away by these awful scourges.