HISTOLOGICAL DEMONSTRATIONS. 59 



or in groups of two or three here and there amidst the 

 rouleaux. Their shape is irregular, and amoeboid movement 

 may possibly be seen. Generally, however, the blood 

 requires to be raised to its normal temperature (38 C.) with 

 the warm stage (Fig. 48 or 49) before the movements can 

 be clearly seen. The size of the white corpuscles varies. 

 Some are twice as large as the coloured corpuscles, others 

 are about the same size. 



c. Fibrin. Very delicate colourless homogeneous 

 threads of fibrin may possibly be found stretching across 

 the spaces between the corpuscles. 



d. Effect of acetic add. Add acetic acid at margin of 

 cover-glass, and if necessary gently raise the cover with the 

 point of a needle to break the coagulum. Observe that 

 the coloured corpuscles become globular, and lose their 

 colour, while the white corpuscles become very transparent 

 and most of them exhibit three nuclei. Sometimes, how- 

 ever, though rarely, there is only a single nucleus, and 

 sometimes there are as many as five. 



80. Crenation of the Corpuscles. Allow a drop of 

 the same blood to remain exposed to the air for twenty 

 seconds or so before applying the cover-glass in order to 

 produce crenation of the coloured corpuscles. A corpuscle 

 thus changed is covered with delicate spinous projections, 

 like a thorn-apple. In most bloods only a few of the cor- 

 puscles become crenated, while in other specimens nearly 

 all the corpuscles undergo this change. Possibly those 

 corpuscles which are prone to crenate have thinner enve- 

 lopes than the others, and on this account more readily 

 permit of the slight exosmose to which the crenation is 

 commonly ascribed. There is reason for suspecting, how- 

 ever, that crenation may be due to some other cause as yet 

 unknown ; for it is regularly produced in such an animal as 

 a dog when poisoned with Calabar bean (Fraser), and in 

 that case it seems unreasonable to ascribe it to any change 

 in the specific gravity of the blood plasma or corpuscles. 



8 1. Effect of Magenta. Add to the same blood, 

 before applying the cover-glass, a drop of the special 

 magenta fluid for staining blood corpuscles ( 324, b) ; mix 



