II.] STRUCTURE OF BLOOD. 41 



the nucleus through the body (if the rays are 

 not seen irrigate with 2 to 5 p.c. salt solution, 

 but in this case be careful not to mistake foldings 

 of the corpuscle for rays). Later the corpuscle 

 becomes spherical and its body colourless. Whilst 

 the earlier changes are taking place some of the 

 corpuscles may be seen to extrude their nuclei. 



8. Dilute a little fresh blood with twice its volume of 

 6 p.c. salt solution ; mount a drop of the mixture 

 and place it aside for an hour or so to clot ; 

 irrigate it with 30 p.c. alcohol and then with 

 Spiller's purple dissolved in water or in dilute 

 alcohol. Note the deeply stained network of 

 fibrin fibrils and the numerous long threads of 

 fibrin running from the broken-down colourless 

 corpuscles. 



B. BLOOD OF MAN. 



With a needle prick the end of a finger, and 

 squeeze out a small drop of blood and mount it 

 (cp. A. 1). Observe the red corpuscles. 



a. They roll about readily, when the cover-slip 

 is lightly touched. 



b. Soon after being taken from the body they 

 stick to one another, and, owing to their 

 shape, usually in rouleaux. 



c. They are biconcave discs. Note that on fo- 

 cussing down on the circular face a darkish 

 centre and a light rim is first seen and then 



