In these columns we have called attention repeatedly to the post hoc ergo propter hoc fallacy in claims advanced in favor of the treatment of various infectious conditions with bacterial vaccines. The majority of the acute and subacute conditions are curable spontaneously without any such specific means as vaccines have been thought to be, and especially when the general condition of the patient receives good attention and when, as in the case of strictly local infections, the proper conditions favorable for healing are secured by surgical measures. In any event, the more chronic infectious processes subjected to vaccine treatment almost without exception present variations in their course; periods of improvement succeed periods of exacerbation.