48 PRACTICAL HISTOLOGY. 



coronary artery and vein and cardiac nerves, easily recognised by their lying together and by 

 their structure. Trace the muscular fibres mapped out into bundles. Some are cut trans- 

 versely, others obliquely, and some longitudinally. Many nuclei are seen, which are the nuclei 

 of the muscular fibres. Select a transverse section of a group of fibres. (H). Observe the 

 polygonal shape of the fibres from mutual pressure, the existence of a violet-stained nucleus 

 in the centre of some of them not in all, and the striae radiating from the nucleus ; a delicate 

 endomysium will also be seen. (Indicate these in PI. IX., Fig. 2.) Select a longitudinal section, 

 observe the faint striation, the branching and anastomosing of the fibres, and the oval, violet- 

 stained nuclei in the course of the fibres. The places where the oblong muscular cells which 

 make up a fibre join, indicated by a transverse line, due to the presence of a cement-sub- 

 stance, are to be looked for. (Indicate the characters of these fibres in PI. IX., Fig. I.) 



Cement-substance. The cement-substance which unites one cell to another may be de- 

 monstrated thus. Thrust the nozzle of a hypodermic syringe filled with half per cent, solution 

 of silver nitrate amongst the fibres of the heart, and forcibly inject the silver solution so as 

 to separate the heart-fibres. Place the heart in alcohol, and after twenty-four hours snip out a 

 small piece which has been acted on by the silver, and after teasing in glycerine expose it to 

 the light and examine for the lines of junction of the cells stained brown or black by the 

 silver. 



Blood-vessels of the heart present practically the same arrangement as in striped muscle, and 

 are prepared and examined in the same way (p. 41). 



Nerves and ganglia of the heart. Sometimes preparations of these are obtained in trans- 

 verse sections of the ventricles ; but to see their arrangement and distribution the heart of a 

 frog, or small pieces of any mammalian heart, must be treated with lemon-juice, chloride of 

 gold, and formic acid, as described at p. xlv. The nerves and ganglia must then be dissected 

 out with the aid of a dissecting microscope (p. xxxv). 



PURKINJE'S FIBRES. 



A delicate network of fine transparent lines is seen, with the naked eye, on the interior 

 of the ventricles of the heart of a sheep or ox. These are Purkinje's fibres. They consist of 

 imperfectly developed muscular fibres they are, in fact, vestiges of what each heart-fibre was 

 originally. They are made up of polygonal-shaped cells, each often with two nuclei, and only 

 the outer half of each cell is striated ; but in the deeper layers, cells are found where the 

 striation has involved three-fourths of a cell, and deeper down still they become continuous 

 with the ordinary heart-muscle. Each muscular fibre of the heart, and in fact, every striped 

 muscle, was originally non-striped, and the striation always begins at the periphery of the cell, 

 so that the fibres made up of these cells represent an embryonal phase of muscular tissue. 



PREPARATION. With scissors or a knife cut out these fine threads and macerate them 

 for two days in dilute alcohol, stain with picrocarmine, and tease a small piece in glycerine 

 until isolated cells or groups of cells are found. 



EXAMINATION (H). Observe the isolated polygonal cells, each with two nuclei, and 

 the outer half of each cell marked with every gradation between these and cells where the peri- 

 nuclear part is completely striated. (Indicate these cells in PI. IX., Fig. 3.) 



