47 





''ERSIT71 





HEART AND BLOOD-VESSELS. 



THE heart is invested by a fibrous pericardium covered by a layer of squames, whose 

 existence is easily demonstrated by the nitrate of silver process. It is lined by a thinner 

 membrane also covered with squames, the endocardium, capable of demonstration in a similar 

 manner. The muscular tissue of the heart is transversely striped, though involuntary. The 

 striae are always more or less indistinct. The fibres branch and anastomose. They consist of 

 short nucleated segments joined by a cement, and are devoid of a sarcolemma. 



ISOLATED MUSCULAR FIBRES OF THE FROG'S HEART. 



PREPARATION. Place the heart of a newly killed frog in a small quantity of a forty per 

 cent, solution of caustic potash (p. xxxiv) for a quarter of an hour. Take a fragment of the 

 tissue and tease it with needles in a drop of potash solution. Be careful to add no water. 

 Cover. 



EXAMINATION (H). Observe the isolated muscle-cells. They are fusiform, and in the 

 broad middle part there is a well-defined nucleus, and the substance of the fibre is trans- 

 versely striped. Do not preserve this. If it be desired to possess a permanent preparation, 

 small pieces of a frog's heart must be placed in dilute alcohol for twenty-four or forty hours, 

 and then stained in picrocarmine ; and, after teasing to isolate individual cells, add glycerine 

 and mount the preparation. 



FRESH HEART OF A MAMMAL. 

 Treat a small piece of the heart of a rabbit in the same way as the frog's heart. Cover. 



EXAMINATION (H). Observe the oblong muscle-cells isolated. Each cell is nucleated 

 and transversely striated. Do not preserve this. 



HEART FOR PRESERVATION. 



PREPARATION. Place small pieces of the heart of a rabbit, or a piece of a human heart, 

 including a piece of the pericardium, in chromic acid and spirit fluid for ten days, transfer to 

 spirit, and then make a transverse section through a ventricle, including the pericardium. Stain 

 a section with logwood and mount it in dammar. 



EXAMINATION (L). Observe the fibrous pericardium stained of a light blue, and note its 

 thickness. Here and there it sends fine processes into the heart, to form a perimysium for the 

 bundles of muscle. It is important to observe the normal thickness of the fibrous covering, 

 and also the normal amount of connective tissue present, as in every organ, to be enabled to 

 judge when there is any alteration in the thickness of the capsule or the amount of the inter- 

 stitial connective tissue. This point is specially important in relation to the pathological 

 histology of organs. Not unfrequently in these trabeculae are to be seen sections of the 



