THE LYMPHATICS OF THE HEART. 195 



Preparation 5, In addition to these silvered 

 preparations, the endocardium should be examined 

 in the fresh state. This is done by dissecting off a 

 piece of the membrane in salt solution and examin- 

 ing it both with and without the addition of acetic 

 acid. Other portions may be teased out with a view 

 to the demonstration of the elastic muscular tissue. 

 The methods for making and preserving these pre- 

 parations are the same as were employed for showing 

 the structure of the coats of the bloodvessels, to the 

 description of which the student is referred (p. 140). 

 It may be noted that in some animals the sheep, 

 for instance the peculiar, large, cubical or oblong 

 cells which form, in series, the fibres of Purkinje will 

 be found in the endocardium. They are about the 

 size of fat- vesicles, which are also found in the endo- 

 cardium in this animal, but the two could hardly be 

 confounded, for the cells forming Purkinje's fibres 

 have a clear or slightly granular nucleated central 

 portion which does not strongly refract the light, and 

 a striated circumference, which is apparently con- 

 tinued into that of the neighboring cells; whereas 

 the fat-cells, although they may also occur in rows, 

 and may be of much the same size as the cells in 

 question, present, by virtue of their strong refracting 

 power on light, a totally distinct appearance. 



Preparation 6. Lymphatic system of the 

 heart. If the fine canula of a Pravaz syringe filled 

 with Berlin blue solution is stuck into the muscular 

 substance of the fresh heart at any part, and the fluid 

 is forced out at the point, the injection will pass 

 freely into the lymphatic interstices between the mus- 

 cular fibres, and if the tube is inserted near the outer 

 or inner surface, will find its way into the lymphatics 

 of the pericardium or endocardium, which can in 

 this way be readily displayed. 



