Endocardial Fibroelastosis of Large Mammals.

Formalin fixed hearts of a blue whale, an Indian elephant, a hippopotamus, a sea lion, a white rat, a mouse, a normal 15-year-old girl, an infant with endocardial fibroelastosis, and three human subjects with myocardial hypertrophy were studied. The quality of fixation and preservation varied from fair to very good. Several sections were made from the lateral part of the left ventricular wall, one-third the distance from the base to the apex, though not all specimens were always from this exact locus. Sections of the left atrium were taken from the lateral wall, half-way between the apex of the left auricle and the left ventricle when possible. The aortas were studied just distal to the aortic ring. The specimens were embedded in paraffin, sections were cut at six microns and were stained with hematoxylin and eosin, and with Weigert elastic tissue stain. With an ocular micrometer on a compound microscope, the diameters of the myocardial fibers were measured in sections which included the nuclei to insure that the measurements were made near the centers of the fibers. In addition, myocardial nuclear densities (the number of nuclei in a circular field with a diameter of 150 microns and a thickness of 6 microns)