which seems to suffice for the purpose; the subtlety and rapidity with which it traverses and impregnates the air; and the keen and quick perception with which it is taken up by the organs of those creatures.  The instance of the scavenger beetles has been already alluded to; the promptitude with which they discern the existence of matter suited to their purposes, and the speed with which they hurry to it from all directions; often from distances as extraordinary, proportionably, as those traversed by the eye of the vulture.  In the instance of the dying elephant referred to above, life was barely extinct when the flies, of which not one was visible but a moment before, arrived in clouds and blackened the body by their multitude; scarcely an instant was allowed to elapse for the commencement of decomposition; no odour of putrefaction could be discerned by us who stood close by; yet some peculiar smell of mortality, simultaneously with parting breath, must have summoned them to the feast.  Ants exhibit an instinct equally surprising.  I have sometimes covered up a particle of refined sugar with paper on the centre of a polished table; and counted the number of minutes which would elapse before it was fastened on by the small black ants of Ceylon, and a line formed to lower it safely to the floor.  Here was a substance which, to our apprehension at least, is altogether inodorous, and yet the quick sense of smell must have been the only conductor of the ants.  It has been observed of those fishes which travel overland on the evaporation of the ponds in which they live, that they invariably march in the direction of the nearest water, and even when captured, and placed on the floor of a room, their efforts to escape are always made towards the same point.  Is the sense of smell sufficient to account for this display of instinct in them? or is it aided by special organs in the case of the others?  Dr. MCGEE, formerly of the Royal Navy, writing to me on the subject of the instant appearance of flies in the vicinity of dead bodies, says:  “In warm climates they do not wait for death to invite them to the banquet.  In Jamaica I have again and again seen them settle on a patient, and hardly to be driven away by the nurse, the patient himself saying.  ’Here are these flies coming to eat me ere I am dead.’  At times they have enabled the doctor, when otherwise he would have been in doubt as to his prognosis, to determine whether the strange apyretic interval occasionally present in the last stage of yellow fever was the fatal lull or the lull of recovery; and ’What say the flies?’ has been the settling question.  Among many, many cases during a long period I have seen but one recovery after the assembling of the flies.  I consider the foregoing as a confirmation of smell being the guide even to the attendants, a cadaverous smell has been perceived to arise from the body of a patient twenty-four hours before death.”]