tokens: In two separate studies , specimens of saliva from 57 individuals over the age of 65 years ( mean age , 76 . 7 years ) and 37 persons under the age of 40 years ( mean age , 28 . 8 years ) were examined for concentrations of IgA as functions of volume , total protein , and electrolyte conductivity ; some were also tested for IgG and IgM content .