In about fifteen minutes after the intra-venous injection of 13 minims of undiluted _Aqua Ammoniæ_, the doctor "was astonished at the calm and painless expression of her _countenance_, so lately _expressive of anxiety and pain_." CASE V. A healthy young girl of 13. She felt a stinging sensation on the [right] wrist, accompanied by itching and redness at the spot [bitten]. For several minutes there was but little pain, but in half an hour a _painful sensation_ began to be felt at the spot, which quickly _extended up the arm to the shoulder_, and, in the course of an hour, _along the neck to the back of the head_. * * * _Pain in the præcordial region, with apnæa_ coming on, I was sent for. When I arrived she was screaming fearfully with _pain_, and frequently exclaiming she would _lose her breath and die_. The _pulse_ had become _thready_ and the _surface cold_. From these _data_ the poison of _Latrodectus mactans_ is suggested for trial in _angina pectoris_, in that its physiological action presents the closest _similimum_ yet found. II. It may be well to offer a critical examination of the foregoing cases. If they are genuine effects of the poison of _Latrodectus mactans_, they must afford a _recurrence of corresponding symptoms_. They may differ in _degree_, because the quality of the venom may vary; first, from the season in which the bite occurred (and judging from cases I, IV and V, the poison of _Latrodectus mactans_ is most virulent in the month of September), and, secondly, from the more thorough elaboration of the venom. It is known that the poison of _Crotalus horridus_ differs in intensity according to the frequency with which the snake has bitten in a given period of time; of four successive "strikes" in four different organisms, and at brief intervals, the intensity of the action will vary, so that while the first wound is lethal the last is not--on which fact depends the vaunted reputation of many an antidote to the bite of the rattlesnake. That this may be also true of the spider poison is the only explanation I can offer for the fact that many naturalists have allowed themselves to be bitten by spiders of reputed poisonous species, and with impunity. RECURRENCE OF CORRESPONDING SYMPTOMS. (_Arabic numerals refer to the Cases._)