This section is from the book "Our Edible Toadstools and Mushrooms and How to Distinguish Them", by W. Hamilton Gibson. Also available from Amazon: Our Edible Toadstools And Mushrooms And How To Distinguish Them.
1. Avoid every mushroom having a cup, or suggestion of such, at base (see Frontispiece, and Plates 3 and 4); the distinctly fatal poisons are thus excluded.
2. Exclude those having an unpleasant odor, a peppery, bitter, or other unpalatable flavor, or tough consistency.
3. Exclude those infested with worms, or in advanced age or decay.
4. In testing others which will pass the above probation let the specimen be kept by itself, not in contact with or enclosed in the same basket with other species, for reasons given on page 69.
Begin by a mere nibble, the size of a pea, and gentle mastication, being careful to swallow no saliva, and finally expelling all from the mouth. If no noticeable results follow, the next trial, with the interval of a day, with the same quantity may permit of a swallow of a little of the juice, the fragments of the fungus expelled as before.
No unpleasantness following for twenty-four hours, the third trial may permit of a similar entire fragment being swallowed, all of these experiments to be made on "an empty stomach." If this introduction of the actual substance of the fungus into the stomach is superseded by no disturbance in twenty-four hours, a larger piece, the size of a hazel-nut, may be attempted, and thus the amount gradually increased day by day until the demonstration of edibility, or at least harm-lessness, is complete, and the species thus admitted into the "safe" list. By following this method with the utmost caution the experimenter can at best suffer but a slight temporary indisposition as the result of his hardihood, in the event of a noisome species having been encountered, and will at least thus have the satisfaction of discovery of an enemy if not a friend.
It may be said that any mushroom, omitting the Amanita, which is pleasant to the taste and otherwise agreeable as to odor and texture when raw, is probably harmless, and may safely be thus ventured on with a view of establishing its edibility. A prominent authority on our edible mushrooms, already mentioned, applies this rule to all the Aqarics with confidence. "This rule may be established," he says: "All Agarics - excepting the Amanitae - mild to the taste when raw, if they commend themselves in other ways, are edible." This claim is borne out in his experience, with the result, already told, that he now numbers over one hundred species among his habitual edible list out of the three hundred which he has actually found by personal test to be edible or harmless. "So numerous are toadstools," he continues, "and so well does a study of them define their habits and habitats, that the writer never fails upon any day from April to December to find ample supply of healthy, nutritious, delicate toadstools for himself and family." The italicized portion is my own, as I would thus emphasize the similar possibilities amply afforded even in the present condensed list of about thirty varieties herein described. In gathering mushrooms one should be supplied with a sharp knife. The mushroom should be carefully cut off an inch or so below the cap, or at least sufficiently far above the ground to escape all signs of dirt on the stem. They should then be laid gills upward in their receptacle, and it is well to have a special basket, arranged with one or two removable bottoms or horizontal partitions, which are kept in place by upright props within, thus relieving the lower layers of mushrooms from the weight of those above them. Such a basket is almost indispensable.