VENTRICLE. BLOOD. 57 



of the elastic wall of the aorta, and the tendo cordis, recognise 

 the cardiac muscle and its mode of attachment to the latter 

 structure, examine the substance of the valve, observe its 

 covering of endothelium. 



Should the section pass through the corpus arantii its structure 

 will be recognised as white nbro-cartilage. 



Ventricle of Sheep. V.S. (p. 2 (d), s. 22 & 24, c. P., m. B.) 

 (L) The myocardium consists of muscle, sub-divided into fasciculi, 

 separated by thin connective tissue septa, is covered on its inner 

 aspect by the thin endocardium which follows all the irregu- 

 larities of the surface and upon the external aspect by the 

 pericardium. The latter often contains much fat. 



(H) The endocardium loose connective tissue, in which are 

 a few fibres of non-striped muscle, exhibits a number of elon- 

 gated oval masses, the fibres of Purkinje; These consist of large 

 polygonal cells, containing one or two distinct nuclei, surrounded 

 by undifferentiated protoplasm. The periphery of each cell 

 is fibrillated parallel to its surface. Trace them into the 

 myocardium and note their transition into cardiac muscle. 

 These fibres occur in ruminants (Purkinje), not in man. 



BLOOD. 15 



Amphibian and human blood. Study these successively 

 in the same manner. Obtain them as follows. 



Amphibian Blood. Frog. Expose the heart of a pithed frog 

 freely, draw it over the edge of a watch glass with forceps and snip 

 into the ventricle. Collect the outflowing blood without admixture 

 of moisture from the skin and touch the blood with covers or hold 

 covers so that the blood may flow upon them. Newt. Dry the tail, 

 snip off the end. Apply covers to the blood that collects on the 

 stump without touching the skin. 



Human. Congest the end of your linger by winding a cloth firmly 

 round it from base to point. With a clean Glover's needle prick the 

 skin near the root of the nail until the blood wells out freely, touch 



