Abstract
Heart and kidney fragments and liver mitochondria and microsomes were prepared for electron microscopy by standard methods. The fixative, dehydration and embedding mediums each were analyzed separately for protein and lipid removed. It was demonstrated that protein and lipid were lost from mitochondria and microsomes and that protein was lost from tissue fragments during their preparation for electron microscopic examination. The significance of these results with respect to investigations concerned with the correlation of function to morphology is discussed.