Neither in Peru, nor in the neighbouring sections of South America, were dogs ever known to be attacked by hydrophobia prior to 1803; but about this time the malady broke out, during the heat of summer, in the valleys of the northern coast, from whence it extended southward along the maritime plains; having arrived at the city of Arequipa in the spring of 1807, while in Lima it was observed between the summer and autumn of the same year. Having collected all the necessary data for disclosing the origin of this disorder, and consulted in writing the physicians and well-informed persons who had witnessed its symptoms, I have clearly learned,—1st. That this disease arose spontaneously from the increased atmospherical temperature of the years 1803 and 1804. It commenced on the northern coast, commonly called _Costa Abajo_, where the air was so heated that Reaumur’s thermometer indicated the temperature of 30° in some of the valleys: the calms were extreme, without the lightest breeze that could ripple the surface of the ocean; animals rushed into lakes and pools of still water to relieve themselves from the sensation of excessive heat; so that the season described by Horace was fully realized: Jam Procyon furit, Et stella vesani Leonis: ... caretque Ripa taciturna ventis. 2. This disorder affected every sort of quadruped without distinction: and such was the degree of phrensy excited by it, that some animals in their fury bit and tore themselves to pieces; and, in situations where the heat was extreme, several men fell ill with all the symptoms of hydrophobia without having been bit. 3. The malady attached itself more especially to dogs, and some of them suffered so mild an attack that their bite was not mortal; but the greater number were severely affected, and propagated the infection to their kind, to other quadrupeds, and to man. The mean and niggardly overseer of a sugar-estate had distributed among his negroes, though advised not to do so, some head of cattle that died rabid; which he did under the impression that they were only _tocado_, or touched with that disease which in hot weather usually affects cattle from the mountains: and the result was, that of the poor negroes who had partaken of this meat, many died with symptoms of hydrophobia. 4. In the towns of Ica and Arequipa the number of individuals who died, after having been bit by mad dogs, was greater, and their cases less equivocal than the preceding.