“Here, in summer, the air of the atmosphere is uniformly clear and cloudless; and the emanations from the earth’s surface, meeting neither clouds nor mists to impede their ascent, mingle with the other atmospherical ingredients, and diffuse themselves freely through the regions of space. The opposite of this takes place in winter. The heat of the sun is always very considerable, or at least sufficient to disengage from heaps of nastiness and rubbish the noxious vapours which putrefaction has generated in them. At sunset these vapours come in contact with the clouds that gather around us, and soon meet the cold air of the approaching night; the consequence of which is, that they are precipitated into the lower strata of the atmosphere, and wafted on the nocturnal breeze into the interior of our habitations. Thus a satisfactory and rational explanation is given, why there should be more sickness in winter than in summer; and by associating this view of the matter with the bad ventilation in the houses of the poor, who from their inability to provide themselves with fuel[43] and warm clothing, are compelled to exclude the free admission of air, we may perceive the reason why at this season the poor are more obnoxious to disease than those whose pecuniary circumstances enable them to protect their homes from the severities of winter by better means than the utter exclusion of the air. “The generality of persons, overlooking the course of atmospherical changes, imagine that the diminution in the number of cases of sporadic fever observable in summer is owing to the abundant consumption of the fruits of this season. We will not deny that the use of fruit may improve to a considerable extent the health of those persons who in winter and spring have been nourished with strong and stimulating aliment, such as is calculated to disorder the digestive functions; but we are far from thinking that to the use of fruits alone are to be assigned all the good effects which the vulgar fancy they derive from them. We know that in other countries not less bounteously supplied with fruit than Chile, though not favoured with so benign a climate, epidemic diseases prevail more in summer than in winter. For these, and many other reasons which it would be superfluous to detail, we consider ourselves authorized to dissent from public opinion on this subject, and to assign the diminution in the diseases of the character alluded to, during the summer months, to causes more in conformity with medical philosophy: namely, the benign state of the atmosphere in summer; the bodily exercise which the different classes of the community indulge in every summer evening; and the wholesome ventilation which they enjoy at this season, their doors being constantly open, and many of them choosing to sleep even in the open air.” APPENDIX ON THE ZOOLOGY OF WESTERN PERU.