Notwithstanding discouragements of many kinds, the test of the efficacy of diphtheria serum was persevered in when others with more apparent reason for interest in it became disheartened and were ready to give it up, if not even actually deprecating its use. The medical profession understands very well now how unfavorable were the conditions under which diphtheria antitoxin was used at first. The original experiments had been made in the laboratory with small animals, and the amount of antitoxin necessary to produce good effects in human beings was not well understood. As {346} a distinguished authority in children's diseases, who is himself a great advocate of the efficacy of antitoxin, once said: "It can practically be admitted that when first antitoxin was introduced its use was scarcely more than expectant treatment." That is to say, so little of antitoxic power was contained in the serum injected at first that the children were practically only kept from other and more exhausting forms of treatment, while the physicians awaited the results with nature as the only really active therapeutic agent. After all, it must not be forgotten that the first doses of antitoxin contained at most 50 to 100 antitoxin units, as we now measure serum efficacy for the treatment of diphtheria. At the present time no one would think of using less than five hundred units as a beginning dose, and those who obtain the best results begin with 1000 to 1500, or in severe cases with 2000 to 3000 units of antitoxic strength. It is almost providential that, notwithstanding this failure to understand the serum properly, the verdict of the profession did not go so generally against antitoxin as to condemn its use hopelessly. It is owing to O'Dwyer and a few other sympathetic souls, who "hoped almost against hope," that finally experience succeeded in demonstrating the true value of diphtheria antitoxin.