When a guinea-pig is treated parenterally with a small dose of any foreign serum, and then, after a period of incubation, receives a second dose of the same serum well below the amount necessary to produce symptoms in a normal animal, this second dose will be followed by severe symptoms, even by death. This increased sensitivity is called anaphylaxis. The casual reader is apt to interpret this statement of the facts as equivalent to saying that a dose of serum sensitizes an animal so that a second dose causes severe symptoms; but the two statements are not identical, and the second statement is not necessarily true, for it omits the essential details. The first sentence states that the animal used is the guinea-pig—an important detail, for some animals are less easily sensitized than others, and some only with great difficulty; white rats, for instance, can be sensitized only when the
WILLIAMS CM. CUTANEOUS MANIFESTATIONS OF ALLERGY. Arch Derm Syphilol. 1934;29(3):333–341. doi:10.1001/archderm.1934.01460090002001
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