Abstract
The oncogenic effect of the murine sarcoma virus (Moloney) was tested in rats. Host-age and virus-dose dependent variations in the pathogenic spectrum were found. Four tumour 'stages' were described: progressively lethal; lethal after long stationary period; complete tumour regression; tumour reoccurrence after complete regression. Virus recovery was highest from the progressively growing tumours and in the reoccurred neoplasms, while no virus was found in stationary tumours or in those sites where regression had occurred. Tumour onset and death was more rapid and frequent when inoculation of the virus was in muscle-rich tissues. When inoculation was into different visceral organs or intravenously, tumour development still occurred primarily in muscle tissue.