“…A 5 Q/o solution of silicon (Silicone M 441, Imperial Chemical Industries, Ltd., Stevenstone, Aurshire, Scotland) in n-heptan was used for this purpose. After incubation, tubes were centrifugated at 4' C for 30 minutes at 800 g. Afterwards, histamine present in the supernatant was assayed biologically on a guinea pig ileum terminalis preparation in a modified Tyrode bath at 37' C. 22,21 Controls were performed each time and samples of blood of rabbits were incubated with equal amounts of saline, instead of antigen. A typical protocol of the experiment is described in Table 3.…”