58 CIRCULATORY SYSTEM. 



the drop with covers. The covers are then placed upon slides or 

 otherwise dealt with as in the sequel. There should be enough blood 

 between the glasses to form a continuous film devoid of air bubbles. 



Freshly shed blood. To retard changes draw a line of olive oil 

 round the edge of the cover and examine at once. 



(//) The formed elements, blood corpuscles or cells, floating 

 in a transparent colourless fluid the blood plasma. Recognise 

 the numerous red and scanty white cells. The latter appear 

 bluish by contrast, and when slightly out of focus more 

 luminous than the red. 



Red blood corpuscles. Examine them (R) carefully as to 

 shape, relative and actual size, colour, contents, and note if 

 there be any varieties. The normal amphibian red cell does 

 not exhibit its nucleus. The nucleus becomes prominent as 

 changes supervene, and is readily extruded from the cell. It 

 is oval, the karyoplasmic network is distinct and colourless. 

 Do not confound escaped nuclei with white cells. 



The human red cells tend shortly to cohere by their broad 

 surfaces, similating piles of coins (rouleaux), probably due to 

 altered surface tension. The form of the individual cell, 

 a biconcave disc, is recognised as it revolves and is seen on 

 edge. On the flat their lenticular shape, i.e., the marginal 

 biconvexity and central biconcavity causes a faint concentric 

 shadow which moves from edge to centre, and inversely with 

 changes of focus. Not infrequently even at first some of the 

 cells are crenated, i.e., have prickly outlines. 



In the course of a few minutes clotting of the blood may 

 occur, when very fine filaments of fibrin will be recognisable 

 traversing the plasma (now serum). Granules are often to 

 be noted at the points of radiation of the filaments. 



