7. _Specific_ forms of pathological atrophy are largely connected with disturbances in the central nervous system. They are often referred to as _trophoneurotic_. Their exact mechanism is not yet understood, and cases may be confused under this head whose remote causes are widely different. Here should be included, for instance, the atrophy of a deep bone which occurs after extensive burn of the surface; also that peculiar form of atrophy of tissues in the stump which produces the so-called _conical stump_. These cases are of a more complicated character, for if pressure is removed from the bone end, especially in young people, the bone tends to grow faster than it should, while the soft parts disappear, partly as the result of mere disuse or loss of function. In this way conicity is produced, which sometimes calls for subsequent re-amputation. Under this head might also be included the so-called “trophic inflammation” (misnomer) of some writers, such, for example, as ulceration of the cornea after division of the trigeminus. The general subject of _atrophic elongation_ also belongs here, referring to the fact that as a result of disuse, or sometimes of active disease, the bones, while showing atrophic changes in other respects, actually increase in length. Should such increase occur in one bone of those portions of the limbs which are supplied with two, the result would be posture deformity and displacement of the terminal portion. CHAPTER II. SURGICAL PATHOLOGY OF THE BLOOD. The part played by the constituent elements of the blood in inflammation, suppuration, and other still more disastrous conditions is so great and so important that, before proceeding to discussion of these lesions, it seems necessary to set forth a _resume_ of facts illustrating the importance of accurate knowledge concerning this most important fluid. The total amount of blood in the human body has been variously estimated at from one-eleventh to one-twenty-fifth of the body weight, the average being about one-sixteenth. The amount which the body may lose and still retain vitality is very vague and differs not only with individuals, but very greatly under various conditions. Severe loss of blood is one to be atoned for as quickly as possible, and is to be prevented as far as it can be after accidents or during operation. For this reason the so-called bloodless method of operating upon limbs, by the use of the rubber bandage, constituted a great advance in surgery. For the same reason the use of hemostatic forceps is of equal value in operating upon other parts of the body; other things being equal the quickest and most satisfactory recoveries follow the bloodless operations, and it is an advantage to conserve this vital fluid as far as possible.