To summarise, my work leads me to believe:o(1)That most children can be immunised within about six weeks of the date of a first injection, or two weeks after the second.(2)That there is sufficient evidence to justify the belief that a single injection may shortly be found to be sufficient to produce satisfactory immunity in nearly every child.(3)That the amount of mineral salt necessary in a sample of A.P.T., or similar antigens, probably has the greatest importance in influencing the antigenic properties of that prophylactic.(4)That the time for relaxation of our efforts to learn more about diphtheria prophylactics is by no means here. Many points yet require elucidation.(5)That the employment of aluminium phosphate for precipitation of the toxoid, and the use of that salt in the injection, leads to far fewer local reactions in the arms than is the case when aluminium hydroxide is injected, as in the case of A.P.T. The almost total absence of reactions when the phosphate is employed leads me to believe that Holt's P.T.A.P. may be found to be a suitable prophylactic to use in the case of adults.(6)That in the case of a few older children, results with only 5 Lf units suggest that, if the mineral content is adequate, the actual Lf dosage necessary for satisfactory immunisation may be very much less than any of us suspected hitherto, even when only a single stimulus is applied. That most children can be immunised within about six weeks of the date of a first injection, or two weeks after the second. That there is sufficient evidence to justify the belief that a single injection may shortly be found to be sufficient to produce satisfactory immunity in nearly every child. That the amount of mineral salt necessary in a sample of A.P.T., or similar antigens, probably has the greatest importance in influencing the antigenic properties of that prophylactic. That the time for relaxation of our efforts to learn more about diphtheria prophylactics is by no means here. Many points yet require elucidation. That the employment of aluminium phosphate for precipitation of the toxoid, and the use of that salt in the injection, leads to far fewer local reactions in the arms than is the case when aluminium hydroxide is injected, as in the case of A.P.T. The almost total absence of reactions when the phosphate is employed leads me to believe that Holt's P.T.A.P. may be found to be a suitable prophylactic to use in the case of adults. That in the case of a few older children, results with only 5 Lf units suggest that, if the mineral content is adequate, the actual Lf dosage necessary for satisfactory immunisation may be very much less than any of us suspected hitherto, even when only a single stimulus is applied.