IMMUNITY AND ANAPHFLAXIS 189 



discovered that the blood serum of an animal actively 

 immunized against diphtheria, when injected into another 

 animal, is capable of rendering the latter insusceptible to 

 what would otherwise be a fatal dose of diphtheria toxin. 

 That is, the serum was able to destroy the diphtheria 

 poison. In conjunction with Kitasato he afterwards proved 

 the same for the tetanus toxin. The transference of the 

 immune serum, in both cases, protects against the specific 

 poison, and so allows the natural resistance of the body 

 to overcome the bacilli. As the new animal body has 

 thus supplied to it an antidote to the microbic toxins 

 which have been shown to produce the symptoms of the 

 disease, no reaction to these toxins occurs (where they 

 have been completely and early destroyed), and so no 

 active immunization occurs. The immunity conferred is, 

 therefore, of a transient nature, and lasts only as long as 

 some of the immune body in excess persists in the blood. 

 Any such excess is destroyed or excreted within eight to 

 fourteen days, and so the immunity may be expected to 

 be absent thereafter. These remarks apply to " antitoxic 

 sera," like those obtained in diphtheria and tetanus. The 

 other form of passive immunization by " antibacterial " 

 or " antimicrobic " sera, has proved unsatisfactory in use, 

 for the reasons given on page 185. The action of the latter 

 sera is not so simple as that of antitoxic sera, but is due 

 to one or more of the following factors : (i) Bactericidal 

 or lysogenic action, that is, death or solution of the micro- 

 organisms ; (2) Opsonic action, or the rendering the 

 bacteria more susceptible to the phagocytic action of the 

 leucocytes ; (3) Agglutinative and precipitative actions, 

 that is, clumping of the bacteria, or precipitation of their 

 soluble products. 



Antitoxic Sera. The actual mode of manufacture 

 may be conveniently given here. Diphtheria antitoxin 

 may be taken as the type. A culture of B. diphtheriae in 

 meat-infusion broth (containing i to 2 per cent of added 

 peptones, and after being made neutral to litmus, having 

 7 c.c. of N /i NaOH added per litre) is incubated for three 

 weeks at 37 C. A strongly toxic fluid is thus produced, 

 which is filtered through a Chamberland candle into a sterile 

 flask, care being taken to avoid exposure to bright light. 



