194 PRACTICAL HISTOLOGY. 



sections. For the teased preparations the heart of a 

 young animal should be chosen, since in these the 

 fibres separate more readily into their constituent 

 cells. A very small shred is placed in a compara- 

 tively large quantity of T V per cent, osmic acid for 

 ten days or a fortnight ; it is then broken up in 

 water as minutely as possible, and the preparation 

 covered and scanned with a high power. Numerous 

 little fragments of varying shapes will be found 

 scattered over the preparation. On careful exami- 

 nation it will be apparent that each possesses a 

 nucleus, which can be made more conspicuous by 

 allowing a little dilute logwood solution to run 

 underneath the cover-glass. These- little fragments 

 of the cardiac muscular tissue, which have the char- 

 acteristic indistinct striation of that substance, are 

 the cells which by their union end to end form the 

 fibres. 



Preparation 3. To show the arrangement of the 

 fibres, and the interstitial tissue and vessels, a piece 

 of the muscular substance is to be placed in strong 

 spirit. In two or three days it will be firm enough 

 to cut. Sections are to be made both parallel with 

 and across the direction of the fibres ; they are to be 

 stained with logwood and mounted in dammar. 



Preparation 4. The endocardium. To dis- 

 play the endocardium the silver method again comes 

 into requisition. That part of the lining membrane 

 covering the septal wall of the right ventricle is the 

 best to prepare, on account of its relative smoothness. 

 The right ventricle is opened in a fresh heart, and 

 the outer wall removed entirely, and then a large 

 piece of the smoothest part of the exposed surface of 

 the septum is sliced oft' with a razor. A part only 

 of the endocardium of the detached piece is brushed, 

 as in the case of the pericardium, and the whole is 

 then washed and treated with silver solution. 

 After three minutes it is put into spirit as before, 

 and when browned and hardened surface sections 

 are cut and mounted in glycerine. 



