Mineral oil injected into the peritoneal cavity of mice tends gradually to disappear. The amount of oil recoverable after a given time depends upon its toxicity, as registered by the carcinogenicity for the skin, refractive index fall, refractivity etc. The 7th day after injection is apparently about the best time to collect the oil.

Loss of body weight of the animal is also a measure of the carcinogenicity for the skin, refractive index fall, refractivity etc. of the oil sample under test. The 3rd day after injection is apparently about the best time to record loss of body weight.

The best animal test for measuring the activity of mineral oils is the injection test, and subsequent determination of the refractive index fall.

The best physical test is to determine the refractive index and viscosity and to combine these in an empirical formula.

A combination of the two tests is the best of all.

The relative amounts of carcinogenic and dermatitic constituents responsible for the general activity can be gauged by a consideration of the viscosity.