The propination to rabbits of fresh milk, umboiled or boiled, soured naturally or by means of colon or aerogenes bacilli does not influence notably upon the weight of the animals. The greatest loss of weight observed in a rabbit to which fresh unboiled milk was given during a certain time, could be attributed to the modification of intestinal flora and its consequences on the animal's health. These results agree with our unpublished observations carried on during the preparation of anticolon rabbit serum, when large amounts of colon bacilli were given to rabbits by stomach tube without any noticeable alteration in the weight of the animals.