[Electronmicroscopic studies on solid mammary carcinomas in bitches]

The electronmicroscopic findings of nine solid mammary carcinomas in bitches are described as well as the observations on tumour cells within lymphatic vessels. In the primary tumours basement membranes surround the cords of tumour cell. In five cases, particularly in two, there are cells with long intracytoplasmic filaments measuring about 65 A thick. The filaments are arranged along the axis of the cells and show focal densities. These cells are presumed to be myoepithelial tumour cells. In eight of the nine tumours there are also carcinoma cells with short single or bundled intracytoplasmic filaments of approximately the same thickness (65 A). These however show no specific order, they are perinuclear or lie in between the organelles. They are called tonofibrillae. Viruses or virus-like particles have not been found.