ic ▁at ▁Joh ns ▁Hop kins ▁University ▁Hospital . ▁Al most ▁immediately , ▁she ▁began ▁collabor ating ▁with ▁Carl ▁Gott fried ▁Hart man , ▁Director ▁of ▁the ▁Car neg ie ▁Institute ▁of ▁Washington . ▁She ▁later ▁joined ▁the ▁Department ▁of ▁Emb ry ology ▁at ▁the ▁Institute , ▁where ▁she ▁was ▁primarily ▁associated ▁with ▁Hart man ▁an ▁expert ▁in ▁o var ian ▁phys i ology ▁and ▁emb ry ology , ▁and ▁later ▁with ▁his ▁successor ▁George ▁Cor ner , ▁co - dis cover ▁of ▁the ▁h orm one ▁pro g ester one . ▁ ▁Both ▁Hart man ▁and ▁Cor ner ▁encourag ed ▁Ball ' s ▁behavior al ▁experiments , ▁which ▁included ▁sexual ▁exc it ability ▁in ▁Rh es us ▁mac aque ▁mon keys ▁across ▁the ▁men stru al ▁cycle ▁( 1 9 3 5 ), ▁the ▁first ▁demonstr ation ▁of ▁sexual ▁re cept ivity ▁in ▁o var ie ct om ized ▁mon keys ▁by ▁in jections ▁of ▁est ro gen ▁( 1 9 3 6 ) ▁and ▁the ▁in hib ition ▁of ▁sexual ▁re cept ivity ▁by ▁in jections ▁of ▁pro g ester one ▁( 1 9 3 9 ). ▁She ▁also ▁documented ▁a ▁case ▁of ▁im itative ▁learning ▁in ▁the ▁mon key ▁( 1 9 3 8 ). ▁In ▁addition , ▁throughout ▁the ▁ 1 9 3 0 s ▁and ▁early ▁ 1 9 4 0 s ▁she ▁published ▁a ▁number ▁of ▁fundamental ▁studies ▁during ▁this ▁time ▁period ▁investig ating ▁sexual ▁behav iors ▁of ▁both ▁male ▁and ▁female ▁r ats , ▁with ▁a