Foreign protein sensitization or anaphylaxis was the basis of Dr. Rutledge's coup. The laws governing this reaction had been more or less worked out by a group of scientists in the twentieth century. They had demonstrated that if a guinea-pig or rabbit were injected with the blood serum of another species, a subsequent dose of an infinitely small quantity of this substance would cause convulsions, collapse and rapid death. Inasmuch as there were many proteins in the atmosphere at that time due to the unrestrained pollination of plants of every description, it was not surprising that they found as many as ten per cent of the white race afflicted with a slight pollen sensitivity which showed up seasonally by causing spasms of the smooth muscle of the respiratory system, a disease popularly called "hay-fever." Since, however, the proteins of the world had always been present, the human race had, by constantly coming into contact with them, become more or less immunized to the majority. Only occasionally a case of violent sensitivity came to light and was recognized as such. Two or three cases there had been which the old scientist discovered while searching the archives of ancient medicine and these gave him the clew he needed. One was the case of a little girl who had somehow or other become sensitized to the protein of wasp toxin and who suffered almost immediate death from anaphylactic "choc" as the result of being stung by that insect. A second instance concerned a woman who went into violent asthmatic paroxysms if a mouse entered the room where she was, and whose skin broke out into large wheals if touched with mouse hair. Finally, and most outstanding in his mind, was the case of a child who was thought to be sensitive to the fish protein in glue and who died almost immediately when the physician testing her had brought a small quantity of the dry protein into contact with a scratch on her arm. These had, however, been rare cases, but they pointed out the method. It had already been proved over and over again that animals could be sensitized experimentally by treating them with foreign proteins, provided that after the initial dose they did not come into contact with the same protein until after a lapse of about two weeks. If they happened to do so the first injection or treatment was frequently neutralized and failed to give the desired sensitivity. With the discovery of a new, highly pure and synthetic protein by Dr. Rutledge the situation with the enemy could be put on a close parallel with the laboratory condition. The enemy could be fed the protein when they were in need of food and had little else, but since it was synthetic, they could not get a second supply until the Doctor was able to put the fatal meal in their way. THE END Transcriber's Note: