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L'étude comparative au microscope électronique de cinq tumeurs carcinoïdes des bronches et d'une tumeur carcinoïde digestive est effectuée dans différentes conditions de fixation. Après fixation à l'acide osmique, les deux formes tumorales se distinguent par la présence de granulations sécrétoires osmiophiles intracytoplasmiques dans les tumeurs carcinoïdes du tube digestif et leur absence dans les tumeurs carcinoïdes d'origine bronchique. Mais après fixation à la glutaraldéhyde on découvre, dans les cellules carcinoïdes bronchiques, l'existence de nombreux grains de sécrétion morphologiquement semblables à ceux de la cellule argentaffine normale ou de la cellule tumorale des carcinoïdes digestifs.

Summary An electron microscopic study of cellular modifications in mammary tissue from post-lactating mice, rats, and rabbits was undertaken. The modifications are due to resorption of previously elaborated and stored secretory material and to degeneration of a number of isolated gland cells.

Summary 0,5 µ thin araldite sections of post-lactating mammary tissue from mice, rats and rabbits have been examined with the light microscope. The study shows more precisely the histological and cytological modifications during the regression process than conventional techniques.

Electron microscopic autoradiography has been applied to the study of protein synthesis in the mammary gland during milk stasis. Thirty minutes after injection of tritiated leucine silver grains are localized over the protein granules in the Golgi vacuoles, in the acinar lumina and in the inter-acinar spaces. They indicate that these granules are newly synthetized proteins and that their passage in the inter-acinar spaces is as immediate as it is in the glandular lumina. The mechanism by which the protein granules reach the inter-acinar spaces has still to be elucidated. The observations indicate that during milk stasis the glandular cell preserves its normal secretory activity.

The protein granules secreted by the mammary gland and first revealed by electron microscopy can be seen in the light microscope, if appropriate techniques are emploied.

An electron microscopical study revealed the presence of virus-like particles in the thymus of adult healthy NZB-mice. The particles are found in the vacuoles of reticuloepithelial cells and are elaborated by a budding process from the membranes surrounding the vacuoles. The formation of B-particles in the thymus of apparently healthy animals is a so far unknown fact the significance of which remains to be determined.

The submaxillary glands of 39 mice and 4 rats are studied comparatively by means of light and electron microscopy. Osmic acid and glutaraldehyde are used as fixatives. The use of the latter favours the discrimination and the study of the two secretory units of the gland: acinus and secretory duct.

Female Sprague-Dawley rats bearing primarily-induced mammary carcinomas were treated with a new immunostimulating agent (P 40). The histopathological modifications encountered in tumors, lymph nodes, liver and spleen are described. Intratumoral injections provoke a more widespread response of the RES, and particularly a more intense reaction in the draining lymph nodes, than systemic treatment.