During recent years, the majority of investigators has been inclined to think that the adjuvant action of different substances is the result of their influence on the cells producing antibodies. However, there is no unity of opinion either on the nature of the changes occurring in the cells, or on their importance for antibody formation. Opinions have been voiced that adjuvants stimulate the cells to absorb the antigen, with or without subsequent phagocytosis; or that they facilitate the liberation of antibodies or, finally, that they augment the total cellular capacity to produce antibodies (1, 2). Some investigators attach great importance to the cellular hyperplasia sometimes observed after the administration of adjuvants (3, 4), although after the introduction of endotoxin cellular alterations may be absent (5).