Numerous efforts have been made to explain the underlying mechanism of bronchial asthma by attempts to reproduce similar symptoms in guinea pigs. Almost invariably the process has involved the introduction of antigenic substances into the respiratory tract of sensitized guinea pigs whose symptomatic and immunological behavior has then been noted. The results of these experiments, briefly summarized, are as follows: When normal guinea pigs were exposed to suitable antigenic substances in the form of vaporous sprays, they apparently could be readily sensitized, for if subsequently injected intravenously with the antigen, they suffered anaphylactic symptoms. This was demonstrated first by Busson (1), and later by others (2) (3). In contrast to this, guinea pigs that were sensitized no matter by what route, and later exposed to vaporous sprays of the sensitizing antigen rarely suffered anaphylactic symptoms on such contact, and then only when supplementary procedures were carried out.