58 PRACTICAL HISTOLOGY. 



a drop of the tannic acid solution near this point. The 

 coloured corpuscles often become globular, and after a time 

 the haemoglobin becomes slowly or suddenly extravasated 

 from the corpuscle in the form of one or more buds adherent 

 to the wall, or in the form of fine granules scattered irregu- 

 larly around the wall. With 1-2 5th inch objective it may 

 be seen, after the action of tannic acid, that the coloured 

 corpuscle has a definite envelope, and this envelope may 

 sometimes be found ruptured where the bud has formed. 

 With such a power as this one may see the pigment rolling 

 away from the envelope like a cloud. It is not always 

 extravasated, but may collect around the nucleus in a 

 stellate mass. This effect of tannic acid was discovered by 

 Dr. Roberts of Manchester. A 2 per cent solution of 

 boracic acid (Briicke) has a somewhat analogous action. 

 For 73, 74, and 75, frog's blood does perfectly, but for 

 76 newt's blood is preferable. 



77. Blood of Bird (H.) a. Observe the pointed, oval, 

 biconvex shape of the coloured corpuscles, and their much 

 smaller size as compared with those of the amphibian. A 

 colourless corpuscle may be seen here and there. 



b. Add acetic acid. A nucleus is revealed in the 

 coloured corpuscle. 



78. Blood of Fish (H.) This blood must be ex- 

 amined in a perfectly fresh condition. The corpuscles 

 resemble those of the bird. The coloured corpuscles, how- 

 ever, are not quite so pointed. 



79. Human Blood (H.) Take a small drop of blood 

 from the finger, cover it immediately, and find the focus as 

 quickly as possible. 



a. The coloured corpuscles. Observe them running to- 

 gether to form rouleaux. Study an isolated corpuscle. 

 Shape ; when seen in front face and in profile. Size. 

 Border. Colour. Transparency. Observe in a corpuscle 

 seen in front face the dark spot in the centre sur- 

 rounded by a light margin, and that when the focus is 

 changed, the centre becomes light and the margin dark. 

 This results from the biconcavity of the corpuscle. 



b. The white corpuscles. Few in number ; found singly 



