Minuteness of detail in relating this case must be excused on account of the extreme interest and importance attached to it. Being brought about under such peculiar and almost unique circumstances it presented the effects of spider-poison in a superlative degree and showed them to be identical with those of snake-poison. But whilst the latter ushers in the symptoms with such rapidity that they cover each other and are difficult of separate analysis, in this case the highly significant paresis of the lower extremities, evidently of central origin, remained separate for some time. Taking this symptom for his guide and interpreting the formidable array of the others, developed during the night, on the same principle, the writer's diagnosis of the case, as it presented itself to him, was paralysis of the motor and vaso-motor nerve-centres. This, he found, and this alone could explain all the symptoms, and he therefore determined to put its correctness to a practical test. There was but one remedy to make this test with and this had to be applied without delay, for the child was rapidly sinking and had almost ceased to breathe. _One twelfth of a grain_ of strychnine was therefore injected in the arm, a bold dose for so young a child, but, as the result showed, exactly the one that was required. The test was eminently successful. Having to leave the child immediately after the injection, the writer on returning in half an hour found his little patient sitting up in bed, perfectly restored, with both poisons so completely neutralising each other, that not a trace of either could be detected. Thus the writer's structure was at last completed, and an insignificant spider furnished the last material required for an important discovery. There are a few hypothetical points yet in the explanation of some of the symptoms of snakebite-poisoning by the writer's theory, but these imperfections are more those of science than of the theory. The whole subject of vaso-motor paralysis for instance, and of the pathological changes that follow it, is more or less a _terra incognita_. Diapedesis is now supposed to be the result of blood pressure, but it occurs in snakebite, where blood pressure is at zero. Feoktistow, we have seen, produced it locally on the mesentery of animals with normal blood pressure, whilst Banerjee arrested by strychnine-injections profuse hæmorrhages from all the mucous surfaces, which were no doubt the result of diapedesis. We know that neither snake-poison nor strychnine affect the nerve ends but only the nerve cells. There must therefore be nerve cells at or near the terminations of the nerves regulating the capillary circulation in the mucous membranes, but microscopical anatomy has yet to find them, for minute ganglia have only been discovered at present in sympathetic nerve ends of the abdomen.