As this can be incontrovertibly ascertained, it is evident, that whatever causes cooperate in producing this different appearance, they produce it by acting upon the _mucosum corpus_, which, from the almost incredible manner in which the cuticle[082] is perforated, is as accessible as the cuticle itself. These causes are probably those various qualities of things, which, combined with the influence of the sun, contribute to form what we call _climate_. For when any person considers, that the mucous substance, before-mentioned, is found to vary in its colour, as the _climates_ vary from the equator to the poles, his mind must be instantly struck with the hypothesis, and he must adopt it without any hesitation, as the genuine cause of the phænomenon. This fact[083], _of the variation of the mucous substance according to the situation of the place_, has been clearly ascertained in the numerous anatomical experiments that have been made; in which, subjects of all nations have come under consideration. The natives of many of the kingdoms and isles of _Asia_, are found to have their _corpus mucosum_ black. Those of _Africa_, situated near the line, of the same colour. Those of the maritime parts of the same continent, of a dusky brown, nearly approaching to it; and the colour becomes lighter or darker in proportion as the distance from the equator is either greater or less. The Europeans are the fairest inhabitants of the world. Those situated in the most southern regions of _Europe_, have in their _corpus mucosum_ a tinge of the dark hue of their _African_ neighbours: hence the epidemick complexion, prevalent among them, is nearly of the colour of the pickled Spanish olive; while in this country, and those situated nearer the north pole, it appears to be nearly, if not absolutely, white. These are facts[084], which anatomy has established; and we acknowledge them to be such, that we cannot divest ourselves of the idea, that _climate_ has a considerable share in producing a difference of colour. Others, we know, have invented other hypotheses, but all of them have been instantly refuted, as unable to explain the difficulties for which they were advanced, and as absolutely contrary to fact: and the inventors themselves have been obliged, almost as soon as they have proposed them, to acknowledge them deficient.