Page:Popular Science Monthly Volume 81.djvu/440

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THE word anaphylaxis is used to designate the train of symptoms and signs which is produced by the incorporation of a foreign soluble proteid into an animal organism which has already been subjected before to the action of this same foreign proteid. The first injection need cause no obvious disturbance at all, and the injected animal seems to be perfectly normal. But if this animal be reinjected after an appropriate interval, it will answer with marked reactions, which may even end in death. Thus, for example, 5 to 6 cubic centimeters of horse serum injected intraperitoneally in a guinea-pig cause no more apparent disturbance than the same quantity of physiological salt solution; but if the same animal receive the same amount of the same horse serum intraperitoneally after two or three weeks, the animal usually dies in a short time. The first injection, therefore, though it caused no obvious change in the animal, has profoundly altered its constitution, and it reacts on second injection as if the original substance were now a violent poison. The animal, however, does not acquire this remarkable property at once; approximately ten to fourteen days must elapse before the second injection elicits marked toxic effects. If the injection is repeated earlier, slight or no symptoms will be produced. It is thus clear that the organism requires a certain length of time before the second injection can call forth toxic symptoms. The whole process, then, shows three distinct phases:

(1) Sensitization, caused by the first injection of the foreign proteid; (2) Incubation, the time which elapses before the second injection can cause a response; and (3) the state of Intoxication which this second injection causes when given to a sensitized animal.

These three stages show some interesting points which deserve to be mentioned more in detail.

Sensitization.—Any soluble proteid may be used to sensitize an animal, provided that it is of foreign nature; nor need these proteids be of animal origin; Wells has recently shown that a large number of plant proteins may be used for this purpose.

The proteid usually employed in laboratory investigation, for anaphylaxis can only be studied by animal experiment, is horse serum, and horse serum is used only because it is easily obtainable, and is not poisonous to the ordinary laboratory animals on first injection. A