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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    swelling of the skin is noticeable. These facts agree very well with the theory according to which the urticarial swellings are caused by a local obstruction to the return of the blood. The increased pressure in the larger veins of the skin (caused by the ligature) overcomes the spasm of the smaller veins. By spasm of the veins he understands a sudden contraction of the musculature of these vessels, which may last a variable time, and disappear quickly or slowly. This contraction must always be greater than the corresponding contraction of the arteries; and the dis- proportion between the arterial and venous tone is the chief factor in the occurrence of spastic oedema. We must include in this group the oedema of erythema multiforme, and the so-called rheumatic and neuralgic oedemas. (Edema occurring in paraplegic and paralysed people must be differently explained. When, in these cases, the vaso-motor nerves of the limb are paralysed, the peripheral vaso-motor centres take over the regulation of the calibre of the vessels ; hyperaamia gives place to anaemia ; and, if the tonus of the veins preponderates, oedema occurs. To this group of nervous oedemas, which have all a more or less local character, the author adds the toxic cedemas. These have all the common property of causing, by some material circulating in the blood, a disproportion between the tone of the arteries and veins. This is seen in morphia poisoning, in curari poisoning in frogs, and in the oedema occurring before death from snake-bites. Until a more plausible explanation be forthcoming, there may be added to this group the oedema occurring in renal disease and scarlet fever. The so-called climatic dropsies which occur, sometimes epidemically, in hot climates may be regarded as of a toxic nature, and something akin to urticaria ah ingestio. Circumscribed, slight, transient oedema (without albu- minuria) is sometimes noticed in people living in the tropics ; this may be caused by an inco-ordination in the tone of the arteries and veins. This increased tone of the vessels is antagonistic to the relaxing effect of the heat; an increased arterial tone would give rise to anasmia, and increased venous one to oedema.