In 1896 Widal and Grünbaum, each working independently of the other, applied the principle of agglutination, as previously recognized by Gruber and Berdet, to the diagnosis of typhoid fever. Since then the Widal reaction, when present, has been considered by most clinicians as the last word in the diagnosis of this disease.
In 1908, however, when Major Frederick F. Russell first began using antityphoid vaccine in the United States Army, and the practitioners over this country gradually followed his lead, a new phase in the diagnosis of typhoid occurred. It was soon recognized by observers that a positive Widal reaction always followed a prophylactic dose of typhoid vaccine. The vaccine, however, had not been in use a sufficient time to ascertain the length of time this reaction persisted. While we now believe the presence of a positive Widal reaction is not necessary for immunity, but that the patient may still