WHAT IS THE SCHICK TEST?
The principle of the Schick reaction is very simple. For a number of years before 1915, the reaction in the skin of guinea-pigs as an index of the neutralization of the standard dose of toxin by the antitoxin was used. If in a test the mixed toxin and antitoxin has an excess of toxin, the skin of the guinea-pig is irritated. If there is an excess of antitoxin, no irritation results and therefore no hyperemic spot appears. In the early investigations of others and of myself on natural antitoxic immunity in man, blood was taken from children and from adults and was tested for antitoxin by the method just described. The results showed that a small percentage of young children and a larger percentage of older children had antitoxin. The idea occurred to Schick that there might be a much simpler way, namely, to introduce