Virginia R. was born on Oct. 4, 1927. At birth, she weighed 7¾ pounds (3.5 Kg.). When examined, she was found to be normal in all respects. There was nothing unusual about her progress, except that she was weaned on the third day, and from then on was fed artificially. On discharge from the hospital at the end of the second week of life, she was gaining normally. When seen on November 8, at 5 weeks of age, she was found to have become pale, although her progress in weight had been good. There was some nasal discharge, and she was thought to have a cold. In all probability, these were the symptoms of the illness which was clearly demonstrated at the next visit, when she was 11 weeks of age. She then had a fever and a cough which had been noted three days before; the pallor had increased