Natural causes of variations in the weight of sarcoma 180.

The weights of mouse sarcoma 180 differed according to the varieties of mouse. In two varieties in which both sexes were studied the tumour weights were lower in females. In three varieties the tumours weighed less at lower environmental temperatures than at higher ones. At three environmental temperatures in the physiological range the surfaces were cooler than the adjacent skin, and the tissues of tumours were cooler than the surrounding subcutaneous tissues. These differences were greater in cooler than in warmer environments and increased as tumours grew larger. There were no histological changes to account for the different tumour weights at different environmental temperatures and it seems probable that tumours are unable to maintain their temperature and their metabolism in cool environments. In mice of the same breed kept at room temperature the smallest animals had the largest tumours in a weight range of 18-28 g.