“…It was thought that difficulty in obtaining food and water due to the behavioural abnormalities probably resulted in the growth retardation and death of the affected animals (Falconer, 1951;Searle, 1952;Snell, 1955;Chai, 1961) (Snell, 1929;Schaible & Gowen, 1961) (Smith & MacDowell, 1930, 1931Kemp, 1938;Osborn, 1938;Marshak, 1938;Francis, 1944Francis, , 1945Ortman, 1956;Rennels & McNutt, 1958;Elftman & Wegelius, 1959;Carsner & Rennels, 1960;Cavallero et al, 1963;Bartke, 1964Bartke, , 1965aBartke, , 1965bBartke, , 1965cBartke, , 1966aBartke, , 1966b. There is evidence to indicate that the high mortality of 'dwarf mice is related to a selective deficiency in the cellmediated type of immunity which is thymus-dependent (Baroni, 1967;Duquesnoy et al, 1970).…”