Selected monographs on dermatology / P.G. Unna [and others].

Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: Selected monographs on dermatology / P.G. Unna [and others]. Source: Wellcome Collection.

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    injections, and urticaria. But if the pressure on the cuta- neous vessels has lasted for weeks or longer, as in atheroma, uric acid concretions, chronic oedema, myxcedema, tumour- like infarcts of the lymph-spaces, such as occur in dermal leprosy—an organic narrowing of the vessels takes place, the whole cutaneous vascular network is diminished, and many capillaries are obliterated. Further on we shall see that this is the cause of many forms of anaemia ; the skin remaining pallid and anasmic, like a cicatrix, after pressure has been removed and swelling has subsided. Local anaemias, due to primary arterial constriction, may be subdivided into those arising from spastic contraction of the arterial muscle-tissue, and those due to an organic nar- rowing of the vessels. The former, of course, are generally temporary, and the latter permanent j but a spastic narrow- ing may occasionally last for some time—hence it is best to retain the division just mentioned. A classification based on a narrowing of arteries on the one hand, and on a con- traction of capillaries on the other, however useful in single cases, cannot be generally maintained; for, although every narrowing of capillaries is not due to arterial constriction, the lessened calibre of an artery always results in a capillary narrowing, at any rate in the stretched elastic skin. Cold is the commonest cause of increased tone in the cu- taneous vessels; but to produce the effect the cold must be considerable, as from an ice-bag or ether spray. If the difference of temperature between the cold body and the skin be inconsiderable, or the abstraction of heat be made difficult in any way, the temporary arterial spasm, in healthy individuals, is followed by a paresis of the vessels, and the heat may continue to be lost. This is the case when the body is submitted to a cold stream of air, or immersed in a moderately cold bath. In fact, there is a subjectively pleasant relaxive hyperaemia, the vessels being expanded beyond their normal calibre, and thus the skin is rendered to some extent inert to the heat-abstracting agent, the in- creased flow of warm blood compensating with accuracy the loss of heat. The effect of slight cold, such as normally acts on the exposed parts of individuals dwelling in northern countries,