He devoted much of his time to the study of the mode of action of Urea-stibamine in Kala-azar and in finding out whether the drug acted directly on the parasite or indirectly through stimulation of the resistance mechanism of the body. [...] The only difference is that while in the case of the lower forms of life, the variety and number of parasites that attack them are limited, in the case of the higher forms of life, the number and variety arc tar greater. [...] The type or types of cells that are rushed to the focus of infection and the numbers mobilised depend upon the nature of the infecting organism and the severity of attack. [...] The dose of antigen, the nature of the antigen, route of administration and the individual capacity to respond to the antigenic stimulus all influence the amount of antibody produced, and the duration of its persistence. [...] For a proper appreciation of the differences in the mode of action of the defence mechanism in different groups of infectious diseases, we must therefore have a clear idea first of the various characters of the parasites that are likely to influence the type of the immunity mechanism brought into action.