242 CLINICAL BACTERIOLOGY. 



This acts by rendering the animal toxin-proof; it contains 

 an antitoxin that enters into innocuous combination with 

 the tetanus-toxin. 



Also after infection, and even after the development of 

 symptoms of tetanus, the serum of the animal may afford 

 protection ; it thus exerts a curative action. To effect cure 

 in animals, however, a much larger amount of serum, or a 

 much more highly active serum, is required than for pro- 

 phylactic immunization ; and the amount of serum required 

 becomes the greater the longer the period of time that has 

 intervened between the intoxication and the employment 

 of the serum. According to observations of Donitz, little 

 more serum is required for the protection of the animal 

 four minutes after the intoxication than in the test-tube for 

 the neutralization of the amount of toxin employed (in the 

 test-tube a serum-dilution of I : 2000, in the body after 

 four minutes a dilution of I : 1 200) ; after the lapse of eight 

 minutes six times the amount of serum will be required 

 (i : 200) ; after the lapse of fifteen minutes twelve times the 

 amount (i : 100) ; and after an hour twenty -four times the 

 amount of serum. 



Serum-therapy in Human Beings. It is obvious that 

 the outlook for serum-therapy in the case of tetanus in human 

 beings is from the outset less promising than it is in that 

 of diphtheria. As it can not be determined from inspec- 

 tion that a wound is infected with tetanus-bacilli, the disease 

 comes under medical observation only after the toxin has 

 already invaded the central nervous system, and has induced 

 more or less extensive and in part perhaps irreparable injury. 

 The cases of tetanus, therefore, thus far treated with serum 

 have not, on the whole, yielded good results. The expla- 

 nation for this may be found in the weakness of the serum ; 

 in view of the lateness of application of the treatment the 

 serum should be of especial strength. Behring has, there- 

 fore, and also in conjunction with Knorr, sought mainly to 

 increase the activity of the serum. To obtain tetanus-toxin 

 he employs horses, which are immunized in the same way 

 as to diphtheria-toxin (p. 218). The tetanus normal toxin, 

 Tet N T 1 , with which Behring starts out, is so strong that 

 one gram contains 1,000,000,000 lethal minimal doses for 

 one gram by weight of guinea-pig (-J- 1,000,000,000 M), 

 1 50,000,000 lethal doses for one gram by weight of mice 

 (-f 150,000,000 Ms), 1,000,000 lethal minimal doses for 



