Nevertheless antidiphtheria serum must not be considered as an antidote; and in pathological diphtheria, the more serum is required the later it is used.[113] In certain cases, if employed too late, it may prove ineffective. [113] BAYEUX: _Thèse de Doctorat_, Paris, 1899. The preventive action of the serum is remarkable. In 10 000 inoculated cases Behring and Ehrlich have had but 10 cases of diphtheria, and these were, moreover, of a benign character. The duration of the immunizing action appears to be from three weeks to two months. This diphtheria antitoxin was first prepared by Guérin and Macé[114] by adding to the antidiphtheria serum a large volume of alcohol, washing the precipitate, and drying it in a vacuum. It is soluble in water, and loses its activity when heated to 65° C. Wassermann[115] has proposed to extract it from the milk of immunized animals, by first coagulating the milk by rennet in the presence of sodium chloride, filtering, and removing the fat from the clear liquid by means of chloroform. After decanting, the clear solution obtained is precipitated by adding to it 30 to 33 per cent. of ammonium sulphate. The precipitate is dried in a vacuum on a polished porcelain slab after having first been strongly expressed. It is then dissolved in water.[116] [114] _Compt. rend. de l'Acad. des Sc._, Apr. 5, 1895. [115] _Zeitschr. für Hygiene_, XVIII, p. 235. [116] ROUX and MARTIN: Contribution à l'Étude de la Diphtérie. _Annal. de l'Instit. Pasteur_, VIII, p. 512. =Tetanus Toxin.=--The fact that the tetanus bacillus never penetrates to the interior of the organism enabled us long ago to foretell that it secretes a very powerful toxin capable of dialyzing and diffusing through the economy. Kuno Faber was the first to fully recognize the fact that the culture bouillon of this bacillus, fully sterilized by filtration through porcelain, possesses an exceedingly high toxicity, and exerts a toxic effect on 50 000 000 times its own weight of living organism. Brieger had previously, however, extracted three ptomaines from the cultures of the bacillus--_tetanin_, _tetanotoxin_, and _spasmotoxin_.[117] In order to obtain a highly active liquid, the same culture medium is inoculated several times in succession, but filtering each time before the new inoculation; the microbes greatly increase in number after each fresh inoculation, and the toxic substance developed by them accumulates.[118] [117] Die Pathogenese des Tetanus. _Berlin. Klin. Wochenschr._, 1890, No. 31. [118] NAILLARD: _Compt. rend. de l'Acad. des Sciences_, CXX, p. 1181. Experiment has shown that the culture bouillon thus obtained contains two kinds of toxic substances[119]--highly toxic alkaloidal bases (ptomaines, tetanin, tetanotoxin, etc.), and a true toxin, possessing diastatic properties, and of almost incredible toxic power. [119] _Annal. Instit. Pasteur_, V, 15.