A carcinoma of the rat (Flexner-Jobling) considered from the standpoint of immunity

Experiments have been in progress for the last year and a half with the Flexner-Jobling rat tumor for the purpose of gaining some insight as to the normal and artifically produced conditions of resistance to this tumor.

The tumor as originally described by Flexner and Jobling was a sarcoma and later became carcinomatous in structure. It has shown no marked variations in histological structure during the eight generations which we have cultivated it. White rats from different dealers varied considerably in their susceptibility to inoculation with this tumor. Animals from the most susceptible source gave 100 per cent. of “takes” whereas the next most susceptible strain gave only 50 per cent. Following inoculation into the region of the axilla metastases occur regularly in the lungs but rarely in the adjacent lymph-nodes. The time of occurrence of metastases would seem to be relatively constant in the most susceptible rats. Metastases occur later and at more irregular intervals in less susceptible animals.