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The kinetics of asphaltenes in crude oils of different stability was studied by confocal microscopy. The physical nature of flocculated asphaltenes of Boscan and Furrial crude oils is shown through of high-resolution micrographics image, and their colloidal structural evolutions are described by an analysis of size distribution of flocculated asphaltenes particles. Two different behaviors associated with the crude oil stability were found. The size aggregates increase rapidly at the first time of the flocculation for a stable crude oil such as the Boscan and gradually for the Furrial crude oil, which is known as a crude oil of low stability. The results obtained demonstrate that the aggregation process of Boscan crude oil is initially determined by the diffusion of the aggregates by the attractive interactions between flocks and aggregate asphaltenes. On the other hand, the aggregation process of Furrial crude oil occurs in the initial stage due to the increment of the number of particles and not by the particle growth until reaching a limited one where the aggregation process becomes governed by the diffusion of colloid particles.

Biopsies of 71 cases of atypical cutaneous leishmaniasis from Costa Rican patients were evaluated by histopathological procedures and attempts were made to culture Leishmania from nine biopsies. Leishmanin skin tests were carried out in 31 patients and 112 healthy individuals. Additional biopsies from 19 patients from Nicaragua were evaluated by routine histopathology. Ten biopsies were studied by confocal and nine by scanning electron microscopy. Inorganic material was analysed using an electron probe for microanalysis. Leishmania parasites were isolated from only two biopsies, but 90.3% of the patients from Costa Rica were leishmanin-positive, as were 27.7% of healthy individuals. Routine histopathological studies revealed naked granulomas formed by differentiated macrophages. Abundant inorganic material was observed in sections examined by confocal microscopy. Electron probe analysis revealed that silica and aluminium were the predominant elements in large particles. We postulate that the presence of this inorganic material, possibly of volcanic origin, in the skin may modulate the immunological response to Leishmania and may inhibit visceralization in the cases caused by Leishmania chagasi.