IN the Yellowstone National Park, the two great herds of wapati or ‘elk’ now comprise about 30,000 individuals, and in the northern area the drought-reduced pastures have accentuated a long-standing problem of over-population (Science Service, Washington, D.C.). The fundamental cause of the food scarcity which has resulted is the inevitable restriction of the natural emigrations of the herds, for outside the northern boundary of the Park, the Yellowstone Valley is occupied by cattle ranches. These make an impassable barrier and confine the deer permanently to a quite inadequate portion of what is naturally only their winter range. Overgrazing has altered the vegetation for the worse; most of the nutritious native grasses have been killed out, and their place taken by a weed grass, fox-tail, which apart from its low nutritive value, pierces the gums and permits the growth of a fungus producing the disease of ‘lump-jaw’. Two solutions have been proposed: one that about half the total number of deer should be captured, transferred to a central slaughtering station outside the Park, and killed and distributed to destitute Indians; the other that the captured animals should be set free in areas of Montana where they could be hunted by sportsmen. The second plan is that favoured by National Park officers, but they insist that whatever plan is adopted, it must be carried out promptly, because of the daily increasing seriousness of the emergency.