Every medical practitioner has experienced the extreme difficulty of adequately controlling epidermophytosis of the feet with the medicaments ordinarily advocated. A new method which gives rapid and consistently satisfactory results must therefore be of wide interest.

1. An analytical study has been made of the mechanism of natural bactericidal action by the serum of various animals (ox, sheep, horse, rabbit, guinea-pig, rat, man) towards certain organisms (B. typhosus, B. dysenteriae Shiga, B. proteus, V. cholerae) exhibiting the maximum reactivity to this effect.2. Serum-complement has no bactericidal action per se, and an antibodylike agent invariably acts as an intermediary agent, “sensitising” the particular organism to the action of the complement and capable of being “absorbed” by it from serum at 0° C.3. This sensitising agent is stable at 55° C. but labile at 60°–65° C. In this respect it resembles natural haemolysins and agglutinins, but contrasts with the more stable immune antibodies and the more labile natural complement-fixing antibodies (for bacterial antigens). It is resident mainly in the carbonic-acid-insoluble fraction of the serum. It is present in the serum of young animals before certain other natural antibodies have developed.4. Absorption tests demonstrate the high degree of specificity of these natural bactericidal antibodies for particular bacteria.5. A non-specific extracellular substance occurs in bacterial cultures which may neutralise or inhibit these antibodies, and interfere with their sensitising action even at 0° C.6. This substance is liberated in large amount in cultures heated at high temperatures (120° C). It can be removed by repeated washing of growths in saline solution. It may inactivate a bactericidal antibody in heated serum, though not in fresh unheated serum, and may inactivate a particular antibody in the serum of one animal species but not in another. Strains of bacteria vary in their production of this substance.7. The observations submitted in this paper, correlated with previous studies of natural antibodies by the authors and others, indicate that immune antibodies have their precursors specifically differentiated in the serum of normal animals and that, in general, immune antibodies are not substances formed de novo.

Since the early work of Nuttall (1888), Buchner (1889), and others first disclosed the bactericidal property of normal serum, a considerable amount of attention has been devoted to this important biological phenomenon. The literature (which has been reviewed recently by Knorr, 1929) lacks, however, a comprehensive and co-ordinated study of the subject, and in fact presents a good many confusing data in regard to the nature of the active principles concerned and their immunological significance.

1. When a solution of commercial peptone is substituted for antigen in a complement-fixation test with the unheated normal serum of certain species (man, ox, sheep, horse, rabbit, white rat), a definite fixation reaction occurs both at 37° C. and at 0° C. In the ox, sheep, horse and rabbit this property of serum is partially stable at 55° C., but normal human serum and the serum of the white rat are inactive after heating at this temperature. The property is resident mainly in the carbonic-acid-insoluble globulins of the serum.2. The same results are obtained when ethyl alcohol diluted with several volumes of normal saline solution is substituted for antigen in a complement-fixation test with normal serum.3. Analysis of these reactions shows a close correspondence with complement-fixation by the sera of normal animals plus the Wassermann “antigen”—the Wassermann reaction of normal animals.4. Marked complement-fixation effects are also obtained with heated normal serum of the rabbit, ox, sheep, horse plus cholesterol suspension, and particularly cholesterolised-peptone, these effects occurring in parallel with those produced by serum plus alcohol-saline, peptone solutions and the Wassermann “antigen.” The heated normal serum of the pig, white rat and guinea-pig do not exhibit these reactions, and the same applies to heated normal human serum. Unheated pig serum fails to react. Such results also elicit a close relationship between these non-specific reactions and the Wassermann reactions of normal animals.5. The reacting property is absent from the serum (heated and unheated) of young rabbits during the first 2 to 3 weeks of life, but appears soon after this (e.g. by the 37th day) and is progressive in development. Its development in early life runs parallel to that of the natural haemolytic property of the serum for sheep's blood (due to a natural antibody-like substance). The two properties are, however, independent as illustrated by absorption tests.6. Besides the agents referred to above as capable of fixing complement along with normal sera, other substances possess a similar property, e.g. certain alcohols, sodium oleate, tissue proteins, certain amino-acids and sodium nucleate. Commercial peptone purified by precipitation with alcohol is equally active with the original material. Cholesterolisation of these agents may yield a product whose activity is greater than that due to summation of effects.7. Wassermann-positive and -negative human sera have been tested in the complement-fixation reaction with certain of these “pseudo-antigens,” viz. alcohol-saline, peptone, cholesterol, and cholesterolised-peptone, but a uniform parallelism has not been demonstrated between the reactions with these agents and the Wassermann effect. Some Wassermann-positive sera react also with alcohol-saline, peptone, cholesterol and cholesterolised-peptone, while sera from selected normal persons are quite inactive. A considerable proportion of Wassermann-positive sera yields definite complement-fixation with cholesterol and cholesterolised-peptone; a small proportion of Wassermann-negative sera reacts with these agents.8. The thermolability of the serum principles acting with various “pseudoantigens” has been studied by testing unheated serum and serum heated at temperatures ranging from 46° to 60° C. Two types of thermolability curve have been demonstrated with different specimens of rabbit serum: (1) a more or less progressive weakening of the various reactions with inactivation at 60° C.; (2) inactivation of the effects with Wassermann “antigen,” alcoholsaline and cholesterol at 50–52° C., activation of the effects with the Wassermann “antigen” and cholesterol at 54–56°C. and inactivation again above 60° C.; in this case the curves for peptone and cholesterolised-peptone do not show such double inactivation. Unheated normal human serum yields reactions with the various agents (including the Wassermann “antigen”) but inactivation occurs at 50° to 54° C. whereas certain syphilitic sera yield thermolability curves somewhat similar to type (1) of rabbit serum, with inactivation at 60° C. or over.

The question of non-specific formation of antibodies is of considerable theoretical and practical importance, and is closely related to the problem of “non-specific immunisation” which has attracted attention in therapeutics during recent years.