Until recently in France the use of prophylactic vaccination against diphtheria has been looked on with suspicion. The experiments which were made in other countries were well known; for example, those carried out in Germany following the first experiments in 1913 by Behring with toxin-antitoxin, then known as T. A. mixture and being of a more or less excessive toxicity. The experiments conducted in the United States on a large scale under the vigorous impulse of such scientists as Park and Zingher were also followed with great attention. But, though they took great interest in the results obtained, especially in the United States, French hygienists did not seem much inclined to use toxin-antitoxin for human active immunization against diphtheria, partly because of the difficulty of its preparation and partly because of the disadvantages of the method used for these mixtures. In fact, the method of preparing the toxin-antitoxin mixture as