Mead has very judiciously observed, "to breed a distemper, and to give force to it when bred, are two different things." He further remarks, that the seeds of the Plague may confine themselves to a house or two during a hard frosty winter, and be preserved, and again put forth their malignant quality as soon as the warmth of the spring gives them force. It is certainly very remarkable that the Plague of London, which commenced at the latter end of the year 1664, should "lie asleep," as Mead says, from Christmas to the middle of February, and then break out in the same parish. It has been also known that an infected bed laid by for seven years had done infinite mischief on being again brought into use. Indeed, it is quite uncertain for how long a period woollen, fur, linen, cotton, and other articles may retain infectious matter in a dormant state. It has been supposed by some that in closely packed bed and body clothes a multiplication of the germs may and does take place, nor do I see any reason why this should not be the case, for these articles contain within their structure the effluvia of the animal body, and they may possibly there find sufficient nutriment for their development. Nees von Esenbeck believed that some of the minute Cryptogamia were re-produced in the air, we are not therefore exceeding philosophical conjecture when we imagine a basis and substratum, though an unusual one, for the germs of vegetation. Exclusion from air and light, {84} however, as would be the case in packed-up clothes, would _a priori_ give a better colour to the conjecture, as these are the usual conditions necessary for the growth of seeds. Small Pox and Cow Pox matter, which are now proved to be the same virus, the former modified by having been through a process of growth and maturation in the cow, are both remarkable for exhibiting their active properties after having lain dormant for a considerable time. And each, though so closely allied, retaining its specific properties. This peculiarity in the history of Small Pox virus suggests a comparison with some phenomena of vegetation, _viz._ that of grafting or budding. The lower Cryptogamia in their fructifications resemble rather multiplication by buds than by seeds. M. Moyen's idea is that every spore or little globule, independently of its neighbouring one, lives, absorbs, assimilates, grows, and re-produces on its own account; this is certainly the characteristic of the Torula and the Uredo, and doubtless is so of many other of the Cryptogamia, the Protococcus nivalis is another instance. Other modes of cultivation produce also great varieties of results of an unexpected kind. Would any one, says Dr. Walker, imagine that cabbage, cauliflower, savoy, kale, brocoli, and turnip-rooted cabbage, were the same species? yet nothing is more certain than that they are only varieties produced by the cultivation of the Brassica oleracea, {85} a plant which grows wild on the sea-shores of Europe.