This point was discussed amongst us--the doctor taking the view that it was always a sign of good blood when one was more than usually subject to the attack of mosquitoes. He was himself an apt illustration of the fact. This statement of course produced a general laugh, and some remarks at the doctor's expense, on the part of the opponents of his theory. Strange to say, old Ike was fiercely assailed by the little blood-suckers. This seemed to be an argument against the doctor's theory, for in the tough skinny carcass of the old trapper, the blood could neither have been very plenteous nor delicate. Most of us smoked as we rode along, hoping by that means to drive off the ferocious swarm, but although tobacco smoke is disagreeable to the mosquitoes, they cannot be wholly got rid of by a pipe or cigar. Could one keep a constant _nimbus_ of the smoke around his face it might be effective, but not otherwise. A sufficient quantity of tobacco smoke will kill mosquitoes outright, as I have more than once proved by a thorough fumigation of my sleeping apartment. These insects are not peculiar, as sometimes supposed, to the inter-tropical regions of America. They are found in great numbers even to the shores of the Arctic Sea, and as fierce and bloodthirsty as anywhere else--of course only in the summer season, when, as before remarked, the thermometer in these Northern latitudes mounts to a high figure. Their haunts are the banks of rivers, and particularly those of a stagnant and muddy character. There is another singular fact in regard to them. Upon the banks of some of the South-American rivers, life is almost unendurable on account of this pest--the "_plaga de mosquitos_," as the Spaniards term it-- while upon other streams in the very same latitude musquitoes are unknown. These streams are what are termed "_rios negros_," or black-water rivers--a peculiar class of rivers, to which many tributaries of the Amazon and Orinoco belong. Our English comrade, who had travelled all over South America, gave us this information as we rode along. He stated, that he had often considered it a great relief, a sort of escape from purgatory, while on his travels he parted from one of the yellow or white water streams, to enter one of the "_rios negros_." Many Indian tribes settled upon the banks of the latter solely to get clear of the "_plaga de mosquitos_." The Indians who reside in the mosquito districts habitually paint their bodies, and smear themselves with oil, as a protection against their bites; and it is a common thing among the natives, when speaking of any place, to inquire into the "character" of its mosquitoes! On some tributaries of the Amazon the mosquitoes are really a life torment, and the wretched creatures who inhabit such places frequently bury their bodies in the sand in order to get sleep! Even the pigments with which they anoint themselves are pierced by the poisoned bills of their tormentors.