Studies on a transplantable chicken tumor (RPL-12 lymphoma). III. Cytological changes during virus-induced oncolysis.

of the RPL-12 lymphoma into the pectoral muscle and brain of the chicken have been described (29, 30). Superimposed infection of the host with the N.F.T. strain of St. Louis encephalitis virus re sults in the development of prominent cytoplasmic â€oeinclusions†• in the tumor cells during the period when the virus concentration in the tumor is high est (30). Apart from some displacement or indenta tion of the nucleus by the â€oeinclusions†• and oc casional margination of the chromatin, there is no further morphological evidence of degeneration before the tumor cells in the pectoral muscle undergo phagocytosis. When the virus is inocu lated into the host with tumor growing in the brain, phagocytosis is deficient, and an abnormally large number of metaphase mitotic figures are observed in the tumor cells containing â€oeinclu sions†• (30). The present experiments were de signed to analyze the formation and structure of the so-called â€oeinclusions,†• and to determine the effect of virus infection on the mitotic process by comparing the cytological and cytochemical properties of the tumor cell before and after infec tion with virus. MATERIALS AND METHODS Complete details of the biological procedures and the plan of the experiments have already been published (29, 30). Tisauea.†" k addition to the routine histological examina tion of all organs and tissues, the following material was specially prepared for cytological and cytocbemical study: (a)pectoral muscle and brain tissue containing tumor, daily from the time of inoculation of virus until tumor cells in the muscle had undergone phagocytosis, or until the birds with tumor in the brain had died; (6) uninfected tumor tissue on the same days as (a). Preparation of the iiaauea.†" Thin fragments were scraped with a sharp knife from the cut surface of the tissue and smeared on slides. When no fixative was used (Table 1), the smears were allowed to dry for 5 minutes before staining; when fixation was desired, the slides were immersed in the fixative while still wet. Small pieces were placed in 0.85 per cent NaCl or mixed with supravital staining solutions on slides and examined directly by ordinary and phase microscopy. Blocks of tissue were fixed as described below, and paraffin and frozen sections were prepared. Except where otherwise stated (Table 1), the final preparations were mounted in Permount, and the paraffin-imbedded material which had been fixed in formol sublimate was treated with iodine …