GROUP

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• XXV

XXV I  . Antitoxins.—These are substances which antago- nize the toxins formed in the body by pathogenic organisms, the toxins of snake venom and other animal poisons, and vegetable toxins such as abrin, ricin, &c . A healthy person can be rendered insusceptible by gradually accustoming him to increasing doses of these poisons, and this immunity is due to antitoxins which are found in the blood-serum and which are products of the blood cells . The nature of these antitoxic substances is not definitely known, but they combine with and destroy the poisons . In specific germ diseases a similar antitoxin forms, and in cases which recover it counteracts the toxin, while the germs are destroyed by the tissues . Antitoxins can be prepared by immunizing a large animal, such as a horse, by injecting gradually increasing doses of specific toxins into its subcutaneous tissue . In due time the horse is bled, the serum is filtered free of blood corpuscles, and then constitutes the anti-toxic serum, which can be standardized to a certain potency . Such serums are injected subcutaneously in diphtheria, tetanus, streptococcic infections, plague, snake-poisoning, cholera and other similar diseases . They do not as a rule harm healthy men even in large quantities, but when repeated they often cause serious symptoms due to the body becoming more sensitive to the action of the horse-serum in which they are contained .