This vast collection of cases is of special interest, because they occurred in private practice. In most of them the nature of the disease was proved by bacteriological examination; in the rest, the clinical evidence was decisive: "It is possible that among the latter we have admitted some streptococcus cases, but the number of such is certainly very small." All other doubtful cases, 244 in number, were excluded. Three thousand three hundred and eighty-four cases were reported by 613 physicians from 114 cities and towns, in 15 different States, the District of Columbia, and the Dominion of Canada. To these 3384 cases were added 942 cases from tenement-houses in New York, and 1468 cases from tenement-houses in Chicago. The New York and Chicago cases were, most of them, treated by a corps of inspectors of the Health Board of the city; and the municipal surveillance was very strict at Chicago:-- "There are very few hospitals in America that receive diphtheria patients.... It was the custom in Chicago to send an inspector to every tenement-house case reported, and to administer the serum unless it was refused by the parents. These cases were therefore treated much earlier, and the results were correspondingly better than were obtained in New York, although the serum used was the same in both cities, viz., that of the New York Health Board." The sum total of results was 5794 cases, with 713 deaths = 12.3 per cent., including every case returned; but 218 were moribund at the time of injection, or died within twenty-four hours of the first injection. "Should these be excluded, there would remain 5576 cases in which the serum may be said to have had a chance, with a mortality of 8.8 per cent. Of 996 cases injected on the first day of the disease, 49 died = 4.9% " 1616 " on the second " 120 " = 7.4" " 1508 " on the third " 134 " = 8.8" " 758 " on the fourth " 147 " = 20.7" " 690 " on or after the fifth " 244 " = 35.3" And in 232 cases, where the day of injection was unknown, there were 19 deaths = 8.2 per cent. "No one feature of the cases of diphtheria treated by antitoxin has excited more surprise among the physicians who have reported them than the prompt arrest, by the timely administration of the serum, of membrane which was rapidly spreading downward below the larynx. Such expressions abound in the reports as 'wonderful,' 'marvellous,' 'in all my experience with diphtheria, have never seen anything like it before,' etc.