A very considerable blight of caterpillars which, in the north of Germany, stripped the gardens and woods far and wide of their foliage, deserves to be here mentioned as a phenomenon appertaining to the lower grades of the animal kingdom[428]. Natural history has shewn that occurrences of this kind are by no means occasioned by new and wonderful influences, but rather by unusual combinations of circumstances, appearing to occur together almost accidentally, at a given time; especially by the simultaneous union of warmth and humidity in the atmosphere, whereby sometimes one and sometimes another of the lower grades of animal existences becomes extraordinarily developed. It is on this account that unusual phenomena in the insect world, whether it be the appearance or the disappearance of particular kinds, take place much more frequently when the order of succession in the seasons and the condition of the atmosphere are in a greater degree than usual and more permanently disturbed; and thus those phenomena have, with much reason, ever been considered as forerunners of pestilences, whenever the human frame has become, through atmospherical causes, generally susceptible of disease. Swarms of locusts have appeared before and during most great pestilences, and indeed the exuberant production of this insect appears, at least in Europe, to require the most unusual combination of causes. SECT. 7.—BLOOD SPOTS. Of rarer occurrence, but quite as important in reference to the general tendencies of life, are _the luxuriant growths of the minutest cryptogamic plants in the water, and on damp things of all kinds_, which, from their spots of various forms and colours, produced the utmost horror both before and during great pestilences, and excited superstitious fears, as appearing to be something miraculous. These spots (signacula), and especially the _blood-spots_, were seen at a very early period, as for instance during the great general plague in the sixth century[429], and again, during the plague of the years 786[430] and 959, when it is said to have been remarked, that those on whose clothes they frequently appeared, and seemingly imparted to them a peculiar odour, were more susceptible than other people of attack from leprosy, on which account this spotted appearance was inconsiderately called the clothes leprosy[431], (Lepra vestium;) not to mention other examples[432] in which plagues affecting the human species did not take place. The same signs also, in the years from 1500 to 1503, threw the faithful into great consternation, because, as on former occasions, they fancied they recognised in them the form of the cross[433]. The phenomenon on this occasion spread throughout Germany and France, and from its great extent and long duration, may be reckoned among the most remarkable of the kind. The spots were of different colours, principally red, but also white, yellow, grey,