The histopathology of the diseases of the skin / by P.G. Unna.

  • Unna, Paul Gerson, 1850-1929.
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: The histopathology of the diseases of the skin / by P.G. Unna. Source: Wellcome Collection.

    42/1250 (page 4)
    time, the resultant anaemia is clue to the locally diminished blood pressure, from the removal of a large quantity of blood. If on the other hand we constrict the limb in a dependent position, from below upwards, by means of an elastic bandage, the blood disappears secondarily, yielding to the primary compression of the vascular system. There follows in both cases on the restoration of the normal circu¬ lation, the familiar hyperaemia of the affected vessels, more marked in the latter case. Prolonged local anaemias of the skin from pressure on the circulation are very familiar. The pressure may be from without, as that of clothes, bandages or instruments, or it may be in or under the skin, as an abscess, an injection or a spastic oedema (Urticaria, Quincke’s (Edema). The ligature of an artery will not cause a local anaemia of the skin so certainly as pressure, on account of the very profuse anastomosis of the capillaries of the skin. In ligature of the main artery of an extremity there is, before the development of the collateral circulation, a temporary anaemia. Related to the pressure anaemias is a group of spastic anaemias of the skin, in which the cause of the partial absence of the blood is to be sought solely in the high degree of contraction of the vessel walls. There is also a pressure anaemia which is not mechanical in its production, like those already mentioned, but of a spastic nature. To a slight pressure, for example, the scratch of a pencil, the normal skin rapidly responds with a hyperaemic streak, which lasts from a half to one minute and is then followed by a similarly shaped anaemia, lasting from five to ten minutes. This depends on the direct irritation of the vessels, and is independent of the intervention of the central ganglia. Within physiological bounds, this process explains the pale colour of the skin in the inhabitants of southern climes, in bakers and machinists and in workers with fire in general. As the cold of the air excites, on the cheeks of the inhabitants of northern regions, a fresh red colour by persistent (compensatory) paresis of the vessels, so the constant existence in the warm air of southern regions causes a habitual (regulating) pallor of the cheeks. Under pathological conditions, this compensatory amemia plays a role in connection with injured limbs where there is a tendency to stagnation and hypostatic congestion. It is the analogue to oedema from increased venous tone on such limbs. Much more important however, is Raynaud’s disease, an idiopathic disease of a spastic nature which affects the ends of the fingers and toes, and belongs to the class of angio-neuroses. The milder forms of this disease are described as “ dead fingers ” or “ local syncope,” the more severe as “ local asphyxia,” but intermediate forms connect these two extremes and a sharp line of division cannot be drawn. This disease, limited to the vessels of the skin and sometimes going on to death of