A doctor is seen examining a young boy in bed. Illustrations of a healthy mouth and a mouth infected with diphtheria bacilli are shown. An illustration of the bacilli is shown. The intertitles note that antitoxin can check the development of diphtheria if given in time. The antitoxin is shown. The process of making antitoxin is shown: bacilli are grown in broth, and are shown some days later. The use of horses in the making of antitoxin is shown and described.