1. Groups of young rats have been fed for periods up to one year on a diet consisting of raw or sterilized milk, with a biscuit made from white flour, to which were added supplements of iron, copper and manganese salts. By this method two samples of commercially sterilized milks, prepared by two different processes, have been compared with the corresponding raw milks drawn from the same bulk supplies.

2. At the end of one year the weights of the groups receiving sterilized milks were about 10 per cent, lower than those of the animals receiving raw milks from the same bulk supplies. This finding is similar to that of Drummond (1933) in a study of the relative values of raw and pasteurized milks by the same methods. It is however in considerable contrast to that of Mattick and Golding (1931) who in comparable experiments found that sterilized milk did not adequately support growth.

3. Animals receiving sterilized milks remained in excellent condition throughout the experiment and they could not be differentiated as regards general health from those which received the raw milks.

4. Adequate reproduction occurred on the raw milks, but no litters were reared. Reproduction was less good on the sterilized milks and, as with the raw milks, no litters were reared.

5. The results with the milk prepared by one sterilization process seemed on the whole better than those from the other; but the evidence was not sufficiently conclusive to make this deduction certain.