the fat was used in food and as a fuel for lighting homes, alongside seal and whale blubber; sinews were used as thread for sewing clothes; the gallbladder and sometimes heart were dried and powdered for medicinal purposes; the large canine teeth were highly valued as talismans. Only the liver was not used, as its high concentration of vitamin A is poisonous. As a carnivore, which feeds largely upon fish-eating carnivores, the polar bear ingests large amounts of vitamin A that is stored in their livers. The resulting high concentrations cause hypervitaminosis A, Hunters make sure to either toss the liver into the sea or bury it to prevent their dogs from being poisoned. Traditional subsistence hunting was on a small enough scale to not significantly affect polar bear populations, mostly because of the sparseness of the human population in polar bear habitat. History of commercial harvest In Russia, polar bear furs were already being commercially traded in the 14th century, though it was of low value compared to Arctic fox or even reindeer fur. The growth of the human population in the Eurasian Arctic in the 16th and 17th century, together with the advent of firearms and increasing trade, dramatically increased the harvest of polar bears. However, since polar bear fur has always played a marginal commercial role, data on the historical harvest is fragmentary. It is known, for example, that already in the winter of 1784/1785 Russian Pomors on Spitsbergen harvested 150 polar bears in Magdalenefjorden. In the early 20th century, Norwegian hunters were harvesting 300 bears per year at the same location. Estimates of total historical harvest suggest that from the beginning of the 18th century, roughly 400 to 500 animals were being harvested annually in northern Eurasia, reaching a peak of 1,300 to 1,500 animals in the early 20th century, and falling off as the numbers began dwindling. In the first half of the 20th century, mechanized and overpoweringly efficient methods of hunting and trapping came into use in North America as well. Polar bears were chased from snowmobiles, icebreakers, and airplanes, the latter practice described in a 1965 New York Times editorial as being "about as sporting as machine gunning a cow." Norwegians used "self-killing guns", comprising a loaded rifle in a baited box that was placed at the level of a bear's head, and which fired when the string attached to the bait was