1. The intramuscular insertion in the rabbit of whole iliac bone, washed iliac bone, and cortical bone from an A-positive dog resulted in the formation of high-titer agglutinins against dog red blood cells. Adsorption tests did not demonstrate any specificity of these agglutinins for the canine A factor in dog red blood cells.
2. In two of five A-negative dogs in each of which was transplanted a knee joint from an A-positive dog, low-titer agglutinins against the donor dog's red blood cells developed. Adsorption tests on the sera of these two dogs suggest the possible specificity of the agglutinins for the canine A substance, although the possibility of the agglutinin being due to a factor other than the canine A factor was not excluded.
3. Transplanted dog bone or its contained cellular elements appears to act as an antigen, but no relation between that action and the blood type of the donor dog could be established with certainty.