We experienced much thunder and lightning for a day or two, which, on the 7th were succeeded by a clear hot day. In the evening, I took a drive in a carriage, in company with Dr. K⸺ to the Lake Agnano. On our way, we passed the Grotto del Cani, or Dog’s Cave, which has the quality of being fatal to that animal when taken into it, whereas the human subject can remain within it uninjured. The cause of this phenomenon admits of easy explanation. A quantity of carbonic acid gas is disengaged from apertures, or chinks in the sides of the cavern, and from its greater specific gravity than atmospheric air, falls to the floor which is somewhat lower than the entrance: it is consequently retained there, producing its peculiar noxious effects on animals of low stature when introduced into it,—as a common-sized dog; while others of a superior height, not having their organs of respiration immersed in the injurious fluid, remain in the cave with impunity. Thus readily does philosophy, in this instance, overturn the errors of superstition; for the peculiarities of this cavern, were formerly attributed to the influence of a vengeful deity. I did not enter the grotto, my friend having neglected to inform me of our approach to it, although the examination of it was a leading object of my evening’s drive. I should, however, have found no gratification, could I have witnessed the convulsive agonies of one of the unfortunate animals, who are kept for the purpose of demonstrating the properties of the cave, and who, after being immersed until life is nearly extinct, are then returned into a purer atmosphere, to reserve them for repeated exhibition. The exhibitors have a peculiar mode of assisting the recovery in this case; namely, to throw the poor creature into the lake. It is not easy to conceive, under suspension of vitality from such a source, how this is to contribute to its restoration. On our return, one of these dogs, consisting literally of skin and bone, was lying on the ground near the mouth of the cave. I could not but wish, that the numerous persons who visit this simple natural phenomenon, would provide themselves with bread to feed these poor animals, instead of wantonly amusing themselves with so cruel an experiment of its effects.