Les manifestations dermatologiques des infections à Yersinia (Y. e. et Y. pst.) sont dominées par l'érythème noueux (E.N.), l'érythème polymorphe (E.P.) est plus rare. La fréquence de l'E.N. (10 à 30 %) dépend de l'âge, du sexe et des variations géographiques ; parmi les causes d'E.N., les infections à Yersinia représentent 10 à 20 % des cas. Dans environ 50 % des cas, il existe des prodomes digestifs (2 à 30 jours avant l'apparition). Les signes généraux sont quasi constants, ainsi que les arthralgies. Les nouures sont souvent étendues, concernant les quatre membres. Elles sont de caractère aigu et très inflammatoire. Leur durée d'évolution est plus courte que celle des autres causes d'E.N. Elle sont parfois associées à des éruptions voisines de l'E.P. Des adéno pathies, bien que peu fréquentes, orientent vers une infection à Y. pst. L'association d'une infection à Yersinia et d'un syndrome de Löfgren est à signaler : les auteurs en rapportent une observation personnelle dans laquelle l'évolution de la sérologie est tout à fait parallèle à celle du syndrome de Löfgren. De rares manifestations cutanées par agresson microbienne directe (Y. e.) ont été également citées. L'histologie des nouures aurait une particularité : l'existence possible de vascularite nécrotique.

Hyperpigmentation of the lower limbs does not always reflect a phlebological abnormality. The authors briefly recall other pathological circumstances which result in cutaneous hyperpigmentation : cutaneous porphyria (hyperpigmentation of the exposed parts), malignant melanoma, Recklinghausen's neurofibromatosis (café-au-lait spots and naevo-cellular naevi), pigmented dermatoses (lichen planus), fixed pigmented toxidermias, drug induced hyperpigmentations (minocyne, synthetic anti-malarials which can provoke the development of large areas of greyish coloured s in), reticular "hot water bottle" dermatitis and malingering syndromes.

The physiological colour of the skin is due, above all, to the presence of melanin in the dermis and the epidermis, but also to the presence of other pigments of endogenous or exogenous origin, such as iron and carotene. The authors present a study of melanogenesis. They review the structure of the eumelanins and the phaeomelanins and recall the steps in their biosynthesis. They examine the functioning of the epidermal unit of melanization, which is a functional unit consisting of a melanocyte, derived from the neural crest, and the keratinocytes which depend on it. The melanocyte synthetizes pigment granules, the melanosomes, which undergo maturation before being transferred and then broken down by the keratinocytes. Finally, the authors study the principal factors which influence the functioning of the epidermal unit of melanization : genetic control, ultra-violet radiation and endocrine factors.

Although clinical studies have been supplying strong arguments in favour of a hereditary transmission of atopy for a long time, the latest works have not made it possible yet to specify the biologic support of this heredity. An obvious correlation, especially, has not been demonstrated between, on the one hand, atopic ground and HLA group and, on the other hand, between a high production of total IgE and HLA group. At present, the production of specific IgE only seems to be really subordinated to the HLA system; it is likely to be the expression of complex immunological disorders of a genetic determinism. Various environmental factors will contribute, on this predisposed ground, to the disclosure or to the worsening of the atopy. Some prevention of atopy may be undertaken. Extended breast feeding, eviction of some environmental nuisance and family affective balance thus represent useful preventive measures. The influence of the date of conception and of the pregnancy and delivery conditions does not appear to be insignificant; but, there, the prevention is more difficult to set up. Finally, the counting of the IgE in the cord blood could lead to the detection of high-risk newborns.