Many of the main facts pertaining to the structure and composition of blood may be easily demonstrated as follows:

1. Kill a frog with ether (note, p. 86); cut off its head, and collect on a piece of glass a drop of the blood which flows out. Spread out the drop so that it forms a thin layer. Hold the glass up against the light, and examine the blood with a hand lens magnifying four or five diameters. The corpuscles will be readily seen floating in the plasma.

2. Wind tightly a piece of twine around the last joint of a finger, then, taking a needle, prick the skin near the root of the nail. A large drop of blood will exude. Spread it out on a piece of glass and examine, as described above for frog's blood. The corpuscles will be seen floating in the blood liquid, but not so easily as in frog's blood, since those of man are considerably smaller.

3. If a compound microscope is available the form, size, and color of human and frog red blood-corpuscles can be demonstrated; also the tendency of the human to aggregate in rolls, and the color, form, size, and relative number of the colorless corpuscles. As any one possessing a compound microscope is sure to know how to mount a specimen of blood for examination with it, or, if not, to have at hand some treatise on the use of the microscope giving the necessary information, details need not be given here.]

4 Obtaining a large drop of human blood as above described (2) ónote: a, that as it flows from the wound it is perfectly liquid; b, that it is red and very opaque; c, spread it out very thin on the glass; note that it then looks yellow when held over a sheet of white paper; d, mix a similar drop with a teaspoonful of water in a wine glass; note that the mixture is yellowish, or, if not, becomes so on further dilution.

5. Place another large drop of human blood, obtained as above indicated, on a clean glass plate. To prevent drying up cover by inverting over the drop a wine glass whose interior has been moistened with water. In four or five minutes remove the wine-glass and note that the blood drop has set into a firm jelly. Replace the moist wine glass, and in half an hour examine again. The blood will then have separated into a tiny red clot, lying in nearly colorless serum.

6. If a slaughter-house is accessible the clotting of blood may be still better illustrated. Provide two large wide-necked glass bottles and a bundle of twigs. When the butcher bleeds an animal collect in one bottle some blood, taking care that nothing else (contents of the stomach, for example, when the animal is bled, as is often done, by cutting off its head) gets mixed with it. Put this bottle aside until the blood clots, and carry it home with the least possible shaking. Next day the mass will exhibit a beautiful clot floating in serum. The latter will probably be tinted red, as the jolting in conveying the specimen from the slaughter-house shakes some of the corpuscles out of the clot into the serum.

7. In the other bottle collect blood and beat it vigorously with the twigs for three or four minutes. Next day this specimen will not have clotted, but on the twigs will be found a quantity of stringy elastic material (fibrin), which becomes pure white when thoroughly washed with water.

8. Take some of the serum from specimen 6. Point out that it does not coagulate spontaneously. Heat it in a test tube over a spirit lamp; the albumen will be coagulated and the whole will become solid.

9. Place a small quantity of whipped blood (7) on a piece of platinum foil. Heat over a spirit lamp. After the drop dries it blackens, showing that it contains much organic matter. As the heating is continued this is burnt away, and a white ash, consisting of the mineral constituents of the blood, is left.