Although the common cold may appear to form a relatively trivial constituent of the mass of acute respiratory disease, which presents the student of preventive medicine with one of his most difficult and pressing problems, the total sickness and incapacity to which it gives rise is by no means small; and there are adequate reasons for regarding it as the occasional precursor of far more serious troubles. It is, therefore, not without interest to enquire, whether or no those procedures, which are commonly recommended as possessing prophylactic value, can make good their claim when submitted to an adequate test. The enquiry here recorded suffers from the fact that the total number of individuals at risk was relatively small; but the answer to the main question posed is so unambiguous, and accords so well with the results obtained in the only other adequate tests of which we have knowledge, that it seems desirable that it should be briefly recorded. It is possible, also, that some little interest attaches to the figures of frequency, duration and severity of common colds within a particular community