Conducting tissues in vertebrate hearts : a histological study

The hearts of representatives of five vertebrate classes ( Pisces, Amphibia, Reptilia, Aves, Mammalia) were stained with hematoxylin and eosin, Masson's trichrome, Best's carmine, toluidine blue, and 2% silver nitrate. Serial sections were made of the hearts of several specimen. A connective band of muscle tissue extending from atrium to ventricle was observed in all specimen studied. The degree to which this connecting muscle tissue was differentiated from the atrial and ventricular myocardium varied with the species. Purkinje fibers were observed in the chicken and some species of mammals. In such genera as Rattus, Mus. and Cants there were no typical Purkinje fibers as described for the genera Bos and Ovis. Comparisons as to types of specialized cells in these genera are given with illustrations. Species variations of the bundle of His in mammals are discussed. A large nerve trunk, not previously mentioned in the literature, was observed in the ventricles of the spade fish (Chaetodipterus faber). Further investigation is needed to determine whether this nerve trunk is characteristic of all advanced Teleostei. A rich ventricular nerve supply with perikarya plus fibers was found to be characteristic of the alligator ventricle, and of the ventricles of all the mammals studied. No perikarya were observed in the turtle ventricle, but there were many nerve fibers. The majority of the ventricular nerve fibers was of the non-medullated type in all of the species studied, although a few medullated fibers were also present. A biochemical analysis of the phospholipids of the specialized tissues of the S-A node and His bundle, as compared to the non-specialized tissues of atrium and ventricle, revealed the former to be much richer in phospholipids. This indicates the order of physiological activity of the heart tissues. Percentages are given for each type of tissue. [...]