9. Since the introduction of the _Röntgen_ or _x-rays_ into surgical therapeutics a new local cause of painful and intractable ulcers should be enumerated. A too prolonged or injudicious exposure of a part to this peculiar influence induces first a dermatitis, which is not always immediate, but may be tardy in appearance, and which may be followed by desquamation or exfoliation that may proceed to absolute surface destruction and sloughing. These lesions are popularly spoken of as _x-ray burns_. The superficial ulcers thus produced may be extensive and are nearly always excessively sensitive and painful. The very structure of the surface vessels is affected and they undergo a species of sclerosis. A strong preparation of _radium_ has been known to produce a similar effect. C. =Constitutional.=--1. Ulcers are frequently met with in certain constitutional conditions which are characterized by tendency to local manifestation at points of least resistance. Among these may be mentioned _scurvy_. 2. There are ulcers of apparently distinctive _trophoneurotic_ origin, of which that mentioned above as B, 8--perforating ulcer of the foot--may possibly be one. These accompany certain nervous disorders of central origin, prominent among which are locomotor ataxia and tabetic disease of all forms. 3. Ulcers are produced sometimes as the result of _specific_ or selective _action of certain drugs_, among them mercury and phosphorus being the most prominent. These manifestations are usually perceived in the mouth, and may be regarded as infections at points of least resistance. Nevertheless, they are commonly associated with the tendency of these drugs. 4. There are many constitutional conditions in which vitality is so lowered that a special liability to ulcer--_i. e._, infection and production of ulcer at many points--is noted. It is well, however, to mention that the common diseases in which this tendency is most often noted are typhoid, diphtheria, diabetes, and syphilis. With this summary of the common causes of ulcer it is again stated that ulcers may be due to direct consequence of traumatic loss of substance or to the process of ulceration--_i. e._, as a consequence of previous infection, or as permitted by trophoneurotic disturbance and ischemia. Ulceration is a process of _molecular death_, in which cells die successively and more slowly, as _distinguished from gangrene_, in which there is simultaneous death of large aggregations of cells, by which a slough or its equivalent is produced.