It is not the purpose of this paper to enter into an exhaustive résumé of the literature pertaining to cutaneous hypersensitiveness, nor to discuss the various theories that have been offered as an explanation of its occurrence. With the exception of a very few observers who explain the phenomenon as an indication of immunity or a phase of anaphylaxis, cutaneous hypersensitiveness is now generally considered to be an evidence of infection, although it is by no means certain that the future will not modify some of the generally accepted views referable to the methods of its production.
In an effort to determine the frequency with which certified milk was infected with tubercle bacilli, in 1916 and 1917, a large number of guinea-pigs was injected with the sediment of this product and the animals studied in the following manner. Several weeks after the milk was injected intradermal tests were made. At