By simply extracting the mucous membrane of the dog stomach or intestine in physiologic sodium chlorid solution, antigens are obtained that differ in precipitin reaction from the proteins of dog serum.
After two days without food, the dog is etherized, bled to death from the aorta, and thoroughly perfused with salt solution after the cava and portal vein have been opened. The mucous membrane is scraped off, washed in water, and extracted for twenty-four hours in a salt solution to which a little thymol has been added. The extracts are neutral in reaction, and with rare exceptions contain measurable quantities of dissolved protein substances, which can be separated into globulin and albumin fractions by means of ammonium sulphate.
Prepared as described, the extracts of dog stomach or intestine may not give any reactions at all with precipitin serums for dog serum or for the isolated dog serum proteins (euglobulin, pseudoglobulin,