ON THE PROPHYLACTIC VALUE OF IODIZED TETANUS TOXIN

It is well known that animals may be protected from tetanus infection by the previous injection of tetanus antitoxin and the immunity thus produced lasts, however, only for a short time (a few weeks). To our regret there has been no safe and practicable method of inoculation against tetanus yet, which confers a long-lasting immunity on animals treated.In the year 1917 Vallee and Bazy published a method of active immunization against tetanus. After demonstrating that injections of tetanus toxin attenuated by the addition of a iodine solution (iodine, 1; potassium iodide, 2; distilled water, 200) conferred a solid immunity on the rabbits treated, they treated 7 seriously wounded persons (who had received prophylactic injections of antitetanic serum) with the iodized tetanus toxin at the military hospital at Begin; the patients received 3 subcutaneous injections at intervals of 5 days, 1c.c. and 2c.c. of a mixture containing 2 parts of toxin and 1 part of iodine solution, and finally 5c.c. of a mixture of 3 parts toxin and 2 parts iodine solution. The French authors concluded that this method of injecting the iodized tetanus toxin is safe and confers a long-lasting immunity.The writer carried out a series of experiments to ascertain the effect of Vallee and Bazy's method. To obtain the tetanus toxin the tetanus bacillus was grown aerobically in "liver-piece broth" with the addition of 10-20 per cent. fresh blood (the blood of cattle, horse or sheep is equally usable), and the lethal dose of the toxin thus obtained is usually 0, 00001-0, 000005c.c. for a mouse of about 10 grams, 0, 0001-0, 00005c.c. for a guineapig of about 400 grams, and 0, 001c.c. for a rabbit of about 2000 grams. As the experimental animals were used a great number of guinea-pigs and rabbits, and a few sheep, goats and horses.The writer found that a mixture of tetanus toxin and iodine solution in proportion of 2:1, as proposed by Vallee and Bazy, is dangerous to guine-apigs and rabbits, the whole of the former (37) and a majority of the latter (7) developing tetanus, and mortality being about 60 and 43 per cent. respectively, while that in proportion of 1:1 is quite safe for both kinds of animals. Two injections of the mixture of 1:1 (1 and 2c.c.) and third injection of that of 2.5:2 (4, 5c.c.) conferred a solid immunity on guinea-pigs treated which resisted the control inocutation of a lethal dose of the toxin, with no reaction.It is much easier to immunize rabbits, one treatment being sufficient for this purpose, when used a dose of 2-4, 5c.c. of amixture of 1:1, 2, 5:2, 2:1, 5, 1, 5:1 or 2, 5:1, 5.In goats the immunity was produced by two injections of 2c.c. of 1:1 and 4-4, 5c.c. of 2, 5:2 or 2, 5:1, 5. Sheep and horses were also immunized by two injections of 5c.c. of 1:1 and 8c.c. of 2, 5:1, 5.The iodized toxin retained its prophylactic value for about 40 days after being mixed with the iodine solution.