If an artery is cut, blood gushes in profusion, lowering arterial pressure. Syncope (swooning) occurs; the hemorrhage decreases; a blood cot forms, sealing the artery; the hemorrhage definitely ceases. Leucocytes and tissue cells invade the fibrin clot and in a few days progressively regenerate the arterial wall. The clot is dissolved and removed.

If an intestine is cut or wounded, the wounded loop becomes immobile. It is temporarily paralyzed so that no fecal matter runs into the abdomen. Another intestinal loop on the surface of the omentum now adheres to the wounded section so that within four or five hours the opening is occluded. Healing is due to the spontaneous adhesion of the peritoneal surfaces, even if the edges of the wound have been drawn together by the surgeon's needle.

A remarkable engineering feat is presented to us in abscess formation. Ordinarily the abscess is limited by a thick protective wall of granulation tissue, which prevents the abscess from spreading and prevents rapid escape of puss into the circulation.

In appendicitis the loops of the bowels around the appendix form friendly adhesions. They adhere together and form a strong wall against further spread of the trouble. Within this enclosure the abscess forms. The line of least resistance, normally, is into the bowels so that practically every case, if not interfered with by meddlesome doctors, will rupture into the bowels and the pus will pass out with the stools.

The potential properties which give to anatomical structures the power to regenerate are actualized within the cells by the physio-chemical conditions in the wound and by the chemical composition of the fluids set free in the tissues. Each tissue is capable of responding, in its own way, at any time in the future, to all physiochemical changes of the blood and lymph in a manner consistent with its own and the body's best interests.

3. The power to immediately reproduce a lost part: A power displayed to the fullest extent by the lower orders of animals, and measurably, by even the highest. This reparative or regenerative power which is common, in a higher or lower degree, to all organic beings, and which was formerly designated by physiologists as the nisus formativus, is a very primitive power. Darwin said: "this power is greater in animals, the lower they are in the scale of organisms." The reason for this lessened reproductive power, in the higher animals, is, that such animals are more complex, the conditions of growth are correspondingly more complex and less easily supplied, when required.

Experiments upon protozoa show that if the cell is divided into two parts, the part containing the nucleus soon again becomes a complete cell with all the properties and powers which it originally possessed. If even a small part of the nucleus remains in the cut-off piece of cytoplasm, reconstruction may take place.

The great utility of many of our garden vegetables,--such as spinach, parsley, cress, etc.--depends upon the possession of a power to repair injuries, so that new shoots speedily take the places of the leaves that have been removed. If a branch is forcibly torn from a tree, or if a cut is made in the tree with an axe, the bark is gradually built up around the wound and cicatrization is finally accomplished.

Heteromorphoses are commonly known in plant physiology. Cut a slip from a willow and place it in the ground and it will develop roots and grow. Either end of the slip may be made the root portion. Many similar examples are known to every one.

Cut a leaf from a begonia plant, place it in a suitable soil and water it; it puts out roots and shoots and in due time a full grown begonia plant results. Cut off a minute part of the leaf, as small as can be seen, and care for this properly, and a full grown plant, just like one grown from the seed, will result. Something like a hundred plants may be produced from the fragments of a single leaf.

The power of regeneration is almost universal, although as we pass from the simplest to the more complex forms of life we observe that this power falls off as organisms become elaborately specialized. Worms, polyps, sponges and other low forms are capable of total regeneration. Fragments of the body are capable of building up a whole new individual, just as are fragments of the begonia leaf. If a nais, or fresh water worm, is cut into fifty pieces, each will reproduce a perfect new animal. The slow-worm reproduces lost parts.

If Planaria are cut into small pieces and the pieces placed where they can absorb nourishment, each of them will grow into a whole worm. If they cannot get nourishment, they cannot grow; each piece, therefore, completely rearranges its materials and becomes a perfect but very minute worm. The piece that happens to contain the pharnyx, finding this too large for its present size will dissolve it and make a new one that fits its new size. Many other worms, when cut, grow new heads or tails.

The tubularia is a kind of sea anemone which grows on a stalk with two rows of tentacles surrounding the head and mouth. If the head with its tentacles is cut off, the first sign of regeneration consists of two rings of lines, one above another, running down the sides of the stem from the cut. These are gradually stripped off keeping one end attached and thus forming new tentacles. The head then forms in their midst. But if before this, you cut off part of the stem, leaving only one of the two rows of lines, the creature, as if in disgust, sometimes erases the one row left and then divides it in the middle thus forming two lines, one end of each, thus forming two very small tentacles, and then grows these to their proper length and size.

A Hydra from which the oral disc and tentacles have been cut, a Nais deprived of its head or of its tail, a snail from which a tentacle with its terminal eye has been amputated, will reproduce the lost parts, sometimes in a very short time--the Hydra, the oral disc with its tentacles; the Nais, the head with its sense organs and special groups of muscles; the snail, the tentacle with its compound eye composed of structures as different as retinal rods, pigment cells, nerve cells, lens, etc. The lobster that has lost its claw, the water newt that has lost an extremity or an eye, the crawfish that has lost a limb or a tentacle will reproduce these as the spinach or parsley reproduces new leaves. Craw-fish can reproduce almost every part of their structure.

The glass snake, which is a lizard and whose family name is squamata lacertilla anguidre ophisarus ventralis, if caught by the tail, will snap it off and hurry on in its effort to escape from its enemy. It then, without trouble or pain, grows a new tail that serves just as well as the original one. The sphenodon and many other lizards can do likewise. Tritons can reproduce an amputated limb, with the numerous differently shaped skeletal pieces of hand or foot, with their appropriate muscles and nerves.