Uji Efek Kelasi Ekstrak Etanol Daun Mangifera foetida L. Dosis 0,5 mg Pada Feritin Serum Penderita Talasemia Secara Ex Vivo = The Ex Vivo Chelating Effect Test of Leaf Ethanol Extract of Mangifera foetida L. in 0,5 mg Dose at Ferritin Serum of Thalassemic Patients