But besides these instances, how many are passing under our own eyes of the disappearance of plants under the influence of cultivation, and the generation of the noxious fumes arising from different and innumerable manufactories. In the vicinity of large cities and manufacturing towns, how rarely do we see healthy vegetation; shrubs and animals drag on a sickly and almost unprolific existence, and their term of natural life is much shortened. And if we compare diseases with this peculiar feature of vegetation, how very close do we find the analogies. The Sweating Sickness which appeared in the latter part of the fifteenth century, and at certain intervals multiplied and extended itself at first only in this country, but ultimately more or less over the continent of Europe, has {92} never since the year 1551 shewn any symptom of productiveness, indeed for all we know the disease may be extinct; on the other hand, it is impossible to say whether or not circumstances may arise, under which it may commence again, to put forth its energies and again desolate the land.[38] Since 1665, the Bubo-plague has not found a congenial soil in this country, or if the seeds be here, which is more than probable, the necessary conditions to excite them to activity do not exist. It cannot be imagined that with all the merchandize which comes into this country from the Mediterranean, but that an abundance of the germs of the disease are annually brought into our ports, and disseminated throughout the land. The law by which we have seen that they possess a power of vitality and reproduction, holds now as it did in former times;--the properties of matter never alter, but the conditions under which they exist may be so modified, as to influence their properties, and the usual course of their operations. It is therefore to {93} an alteration or modification of conditions that we are to look for the exemption, during the last two centuries, from an invasion of the Plague. To say what those conditions may be in their totality is difficult, perhaps impossible. We may generalize on the subject, and imagine the reason discovered, but all those causes which were said to have conspired to favour the spread and contamination with Plague, were as distinctly specified and attributed, as the cause of our late infliction with Epidemic Cholera. Why then did we have the Cholera and not the Plague? To what particular element was it--in the mode of living, of destitution, of filth and want of drainage--can it be ascribed that we suffer under one disease, and not under the other?