This paper records the results of further studies on typhoidin made since the publication of the original article of Gay and Force.
Since Gay and Force1 have reviewed the work on the application of preparations of the typhoid organism to the skin which had been published previous to their article, we shall confine ourselves to a review of observations on typhoidin which have appeared since that date. The original typhoidin employed by Gay and Force consisted of a ten-day culture of a single strain of Bacillus typhosus on glycerin broth evaporated to one-tenth volume. On account of deterioration of the preparation in this form, Gay and Claypole2 precipitated the original typhoidin with twenty volumes of alcohol, filtered, washed with absolute alcohol and ether, and then dried on porcelain plates over sulphuric acid in a vacuum. With a freshly prepared suspension of this typhoidin powder in phenolated saline, equivalent