For several years we have been studying skin reactions produced by a variety of bacterial filtrates in healthy persons, and in patients with different diseases. The recent typhoid epidemic in Montreal seemed to offer an unusual opportunity for further observations on the result of skin reactions with typhoid filtrates in typhoid fever patients. Through the courtesy of Dr. Ralph Lynch, of the Montreal General Hospital, observations were made on skin reactions of 22 typhoid patients in different stages of the disease. Intracutaneous tests with typhoid filtrates were also observed in other groups; for example, those who had no history of typhoid fever or of antityphoid vaccination, vaccinated persons, patients with other diseases, and 4 typhoid patients in Chicago.After preliminary tests, the following technic was adopted: The typhoid bacillus employed in the test was the Rawling's strain. The medium used for the bacterial culture was a sugar-free, beef infusion broth 1% peptone, pH 7.4, to which was added 0...