It is now over twenty years since the first attempts were made to treat patients suffering from acute lobar pneumonia by means of serum obtained from animals immunized to pneumococcus. In 1904 Anders1 collected the reports of 535 cases treated in this way. He concluded that the practical results obtained by the use of antipneumococcus serum did not warrant its general use. Nevertheless, the theoretical study and practical application of antipneumococcus serum have not ceased. Although it has been impossible to demonstrate any striking lowering of mortality in a large series of cases, yet certain good clinical observers have felt that in certain individual instances the results were striking. The experimental evidence, moreover, has been sufficient to inspire hope in the minds of many. It has become evident, however, that the problem can be solved only by more refined and critical methods than those previously employed.
It has been