As the use of antipneumococcus horse serum becomes more extensive, cases are met with wherein sensitiveness to serum complicates its administration, as happens with the therapeutic use of other serums. The reaction induced by giving horse serum to such patients may vary, depending on several factors, among which is liability to "horse asthma." Patients with this condition complain that proximity to horses, whether currying them, driving them, or even going into stables, may bring on symptoms which are typical of bronchial asthma, due doubtless to suspended particles of horse dandruff or horsehair. Walker1 has found that most patients suffering from this condition give positive cutaneous reactions to horsehair proteins, whereas in addition a much smaller number (22 per cent.) react to horse serum proteins. Woodehouse2 has established the fact that the fractional portions of the protein mixture hair, may sensitize, or rather, that its administration results in multisensitization to its