The cytology of the contagious (venereal) tumour of the dog

1. The contagious venereal tumour of dogs has been examined for the first time by modern cytological technical methods and the cytoplasmic structure revealed. 2. Adequate technique, controlled by observations on the living cells, shows that these tumour cells are exceedingly rich in lipide globules, the presence of which has been overlooked (a) because they are dissolved out from paraffin sections and (b) because in frozen sections they are refractory to the customary methods for the demonstration of fatty substances. To stain these globules, the use of a specially devised acetic-carbol-sudan method is recommended. 3. Previously employed methods of studying the tumour cells have been misleading - as indeed they were doomed to be - not merely because of failure to demonstrate the lipides, but still more because of the extensive artefacts which result from failure to take precautions against shrinkage of the cells which follows dissolution of this constituent, which occupies so large a part of the cytoplasm. Current views - that the contagious venereal tumour is composed of round cells or of stellate cells (reticulum cells) - depend entirely on the examination of material showing such fixation or rather post-fixation artefacts. 4. The cell membrane is highly developed and the cells are polygonal in shape and closely aggregated together as in an epithelium. 5. The granules (mitochondria?) are distributed throughout the cytoplasm and are less constantly stained by the classical mitochondrial techniques than are the mitochondria of most other cells. Technique suitable for their demonstration is described. 6. The Golgi apparatus is well developed and has the form of a spiked wreath, one-third to one-half the size of the nucleus. 7. The centrosome and the achromatic spindle have been demonstrated and described. Measurements of the spindle angle reveal a mean value of 114°, contrasting with the angle of cells of the lymphoid series as measured by Ellermann. 8. Routine diagnosis of the contagious venereal tumour is more rapidly and certainly accomplished by means of teased preparations than by the usual sections. Pitfalls in the differential histopathological diagnosis have been explained, especially from mastocytoma and endothelioma. 9. According to present conceptions of the structure and habitus of large lymphocytes (lymphoblasts) it would be difficult to identify the tumour cells with these elements. 10. Accordingly, further support is provided for the author's alternative theory that the contagious venereal tumour may be an apolar neuroblastoma.