The microscope has done good service in the investigation of snake-poison. It has, in the first place, informed us with absolute certainty that there are no micro-organisms or germs of any kind in the fresh poison immediately after it leaves the gland. But a still more important revelation we owe to it is the fact that these organisms, when we introduce them into a 2% solution of the poison, do not die, but live, multiply, and enjoy their existence most lustily, as they do in any other non-poisonous albuminoid liquid, whilst animals of a higher type--say a snail or a frog--soon perish in it. In watching the movements of the latter we find that they get slower and slower, and finally cease. We now follow up the interesting research, and take two frogs. Under the skin of one of them we inject a few drops of the poison solution, the other one for comparison we leave intact, and place both into a glass globe partly filled with water. In a very short time we have no difficulty to identify the poisoned frog. Its hind legs begin to drop and their movements become sluggish. This difficulty increases from minute to minute, until at last all motion ceases, and the legs hang down completely paralysed. At the same time we observe that the animal shows increasing difficulty of breathing, that, even when taken out of the water, and placed on the table before us it gasps for breath and is unable to move. At last respiration ceases altogether and the frog dies. Two problems now present themselves for solution. In the first place we have to account for the fact of the snake-poison leaving the lower forms of animal life intact and being fatal to the higher ones. The symptoms we have observed in the frog point unmistakably to an affection of the nervous system as their cause. Now we know that the lower forms which the poison does not affect have no such system, and we are justified to infer that to the absence of this system they owe their immunity. This inference leads us on to a second one equally justifiable, namely, that there is a certain unaccountable attraction between the delicate nerve tissue and the subtle ophidian poison, which renders the latter a specific nerve poison.