“…They then compared the serum of patients before and after injection treatment and found that mixtures of ragweed extract and post-treatment serum did not give an immediate reaction when injected into the skin of normal recipients, whereas, pretreatment serum, containing as much or even less skin-sensitizing activity, did. At about the same time, Sherman, Hampton and Cooke reported that blocking antibody readily passed the placenta [106], further differentiating blocking antibody from reagin. They interpreted these findings as '.…”