This report may be summarized as follows: a) Toxin-toxoid which failed to combine with antitoxin produced significantly higher antitoxin titers in sheep than did prototoxin-toxoid. b) Toxin-toxoid loses most of its ability to combine with antitoxin in a relatively short period of time (14 days) although some may be retained for as long as 71 days; prototoxin-toxoid, however, retains its combining and precipitating power for a much longer period of time. c) Both toxin and prototoxin combine with antitoxin. d) In the agar diffusion technique a single common zone of precipitation developed between the antitoxin and prototoxin, toxin and prototoxin-toxoid. Toxin-toxoid failed to develop a visible band at a time when prototoxin-toxoid was fully precipitable. e) When either toxin or prototoxin was exposed to 0.5% formalin the toxicity disappeared within 14 days. The combining power and precipitability disappeared relatively soon in the toxin-toxoid but not in prototoxin-toxoid.
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