6. Ulcer is the occasional result of embolic or other disturbance of the principal artery of the part, by which nutrition is cut off and tissue death results.
7. Bites of insects or other parasites or of noxious animals frequently lead to ulceration.
8. Certain more specific forms of ulcer are described by some writers, apparently with more or less reason, among them being chancroid, perforating ulcer of the foot, etc. (Chancroid is described in Chapter X.) Trophic ulcers of the fingers or hand are also seen, particularly after injury to or division of nerve trunks in the arm or forearm. Perforating ulcer of the foot is a circumscribed circular ulcer with thickened edges, often nearly concealed by overhanging skin. It may be found in any part of the sole of the foot, but is most common near the first joint of the great toe. The borders of the ulcer are usually anesthetic. It is frequently seen in diabetics. By some it is associated with trophic nerve disturbance; by others it is regarded as having a specific etiology of its own. The probability, however, is that it is simply a subvariety of pressure sore.
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.