Observations on the Formation of Wheals. IV. Influence of Calcium Concentrations upon Histamine Wheals.

We 1 reported that an unidentified substance could be extracted from the skin of dogs which is capable of augmenting histamine wheals. We have now identified this substance as calcium in a certain zone of dilution and only within this zone, as follows:

The proteins in the water extract were precipitated by alcohol. The alcoholic filtrate was evaporated and the residue extracted with water. The active substance was precipitated from this solution by mercuric acetate. It was redissolved in fresh water when hydrogen sulphide was passed through the mixture. The active principle in solution was further separated from organic impurities, phosphates, etc., by treatment with mercuric sulphate and barium carbonate according to the method of West and others. It was found in the filtrate after this process. When this solution was dialyzed against pure water in a thick collodion sac, the active principle did not pass through, but when redialyzed in a thin collodion sac it was recovered from the dialysate. Advantage was taken of this fact to separate the active principle from practically all remaining impurities. Evaporation of the solution after these steps revealed a few crystals which, although small, were suggestive of calcium sulphate. These resisted ashing temperatures although an earlier ashing of an impure fraction had caused the activity to disappear.

With attention focused upon calcium sulphate, experiments were tried in which this pure salt in very weak concentrations was used in place of skin extract. This, too, was found to have an augmenting effect on histamine wheals. Other calcium salts had a similar effect. An interesting similarity in the behavior of calcium sulphate and skin extract was observed. When skin extract was added to histamine solutions it was noted that the size of the wheals was not in proportion to the concentration of the extract. Often one to 10 dilutions of the skin extract produced a larger augmentation than was obtained with the normal concentration, whereas, concentrated extracts often produced less augmentation.