They are engendered either by external and especially by mechanical influences, or else by various internal causes which may, in like manner, operate mechanically.

To the former belong:

1. Simple or complicated injuries from penetrating mechanical violence, with or without loss of substance; - incised, punctured, contused, gunshot, bitten, and lacerated wounds; - solutions of continuity occasioned by fire and cautery.

2. Imperfect and complete laceration and rupture of solid as also of hollow organs, consequent upon concussive violence, - especially when in the condition of repletion and of distension, - lesions of continuity frequently unaccompanied by perceptible injury to the common integuments and to the parietes of the implicated cavities of the body. The casting of the envelopes of particular organs caused by similar violence, as the separation of periosteum, of the dura mater, from bone, of the fibrous capsules (tunicae albuginese) of certain viscera, as of the spleen or kidneys, - is of like significance.

3. Simple and complicated fractures of bones, incurvation of soft, rickety bones, casting of the epiphyses.

Separations of continuity from internal causes are dependent upon various contingencies. Where mechanical influence is simultaneously at work, the two influences co-operate in such wise that where the one predominates, less of the other suffices to produce the effect. Their occurrence may be rapid or slow. They are brought about -

1. By Violent Exercise

By Violent Exercise of the voluntary and involuntary muscles, lacerating either these or their tendons, or even affecting the bones, - in convulsions, for instance.

2. By Excessive Distensions Of Hollow Organs

By Excessive Distensions Of Hollow Organs, as in laceration of the intestine, of the urinary bladder from accumulation of its contents through paralysis, through mechanical obstruction, stricture, closure, etc.

3. By Hemorrhage

Here the lesio continui consists in great laceration, contusion, disruption, destruction of texture; take, for example, apoplexy of the brain, of the liver, of the muscles; the forcible separation of the strata composing a membranous organ; the loosening of the enveloping membrane of organs, of the periosteum from bone, of the tunica albuginea, through extravasated blood.

4. By Atrophy

When favored by a mechanical influence it occasions a rapid lesion of continuity in the shape of laceration, - or else, being itself caused by pressure and tension, it serves in the long run to produce lesion of continuity, more especially in the muscles and nerves. Under this head should be mentioned the spontaneous casting of normal and of morbid formations, owing to defective nutrition, as of the hair, the nails, the teeth, horny excrescences, and the like.

5. Separation Of Continuity

Separation Of Continuity is the final result of high degrees of diminution of consistency, especially in true softening, the consequence of textural disease. If, therefore, any mechanical cause be requisite at all, the slightest, - even the degree ordinarily in operation, as for example, repletion of a hollow organ, suffices to produce the effect. Amongst textural diseases, inflammation - from its effects in the loosening of tissues, - and the fatty degeneration of muscular organs, more especially of the annulo-fibrous tunic of arteries - stand pre-eminent.

6. In Fine, Lesions Of Continuity

In Fine, Lesions Of Continuity are engendered in primary textures, as well as in new growths, by various processes of liquefaction and dissolution, especially by suppuration and gangrene. To this head belongs, amongst others, the spontaneous separation of dead parts, for instance of fingers, of entire limbs, of heterologous products, such as fibroid and cancerous growths. Lesions of continuity are, upon the whole, simple, or else more or less associated with loss of substance. Their cure is effected by the immediate union of the edges or surfaces of the wound, or, in the case last alluded to, by regeneration.