PRACTICAL HISTOLOGY. 



[ill. 



Fro. 72. Human Red and White Blood-Corpuscles. 

 a. Ued corpuscle seen on the flat ; b. In profile ; 

 c. A rouleau; d. Three-quarter face; e,f. Crenated 

 corpuscles ; g. Spherical ; in. Slightly crenated ; 



of these bodies resembling a pile of coins is produced (fig. 72). 



This is the so-called formation of rouleaux (fig. 72, c). In order to 



obtain rouleaux a fairly 

 large drop of blood must 

 betaken. These chains by - 

 and-by increase in number 

 and intersect each other, so 

 as to produce a network -like 

 appearance in the field. In 

 the rouleaux all the cor- 

 puscles are seen edgeways. 



(b.) Move the preparation 

 until a part of it is found 

 where the red corpuscles 

 are to be seen not in 



L. Large wliite "corpuscle ; I. Small" white cor- rouleaux, but isolated and 

 puscle; p. Granular leucocyte; n. Free granula- , . ,-, a , 



tions, x looo. lying on the flat. 



Study a Single Red Cor- 

 puscle. Observe its shape ; when seen on the flat it is circular in 

 outline, and on bringing its edge sharply into focus, a darker area 

 is seen in its centre (fig. 74, a). If the fine 

 adjustment be used, so as to bring the lens 

 nearer the corpuscle, the dark centre is replaced 

 by a lighter area, while the rim becomes darker 

 (fig. 74, b). 



Sketch the two appearances. 

 This is due to the fact that these bodies 

 are In-concave circular discs. The dark area 

 in the centre is not due to the presence of a 

 nucleus, as -they are non-nucleated. 



This is confirmed by examining a corpuscle 

 seen on edge, when it appears somewhat dumb- 

 bell shaped (figs. 72, b, 73, 2). 



In size they are much smaller than those of Amphibia, being only 

 of an inch (7.7 /x) in their greatest diameter. Their border 

 is smooth, rounded, and regular, their colour is 

 pale straw-yellow, their surfaces are smooth, and 

 they are homogeneous throughout. As to trans- 

 parency, the outline of one corpuscle can be seen 

 through one overlapping it. They are soft and 

 flexible, so that if they impinge on other objects 

 they may change their form, which they rapidly 

 regain, so that they are elastic. 



(c.) Measure the actual size of several corpusekfj 

 by the method described at p. 20. It will be found that all tho 



FIG. 73. Red Blood-Cor- 

 puscles. Human ; i. 

 Seen on their surface ; 

 2. Seen edgeways ; 3. 

 United into a rouleau. 



FlG. 74. Red Cor- 

 puscle seen on the 

 flat. a. On rais- 

 ing, and b. On 

 depressing the ob- 

 jective, x 1000. 



