88 PRACTICAL HISTOLOGY. 



and then with a common knife remove a slice of the spongy 

 tissue. Place it on a slide in a drop of salt solution. With 

 needles detach the bony spicules from the marrow and 

 throw them away. Cover, and examine. 



Most of the cells in the preparation are the proper 

 marrow cells of Kolliker. These somewhat resemble white 

 blood corpuscles, but when acted on by dilute alcohol or 

 acetic acid, they usually exhibit a single nucleus, and often 

 also yellowish particles. Large multi-nucleated masses of 

 protoplasm, commonly termed giant cells (the myeloplaxes of 

 Robin), may be found here and there. They vary in size 

 from five to twenty times that of a blood corpuscle. In a 

 section of the cancelli of decalcified bone of a somewhat 

 young subject, a giant cell may be found in contact with 

 the osseous tissue here and there amongst the osteoblasts. 

 Believing that they are concerned in the absorption of the 

 neighbouring bone which often appears as if scooped out 

 Kolliker has named them osteoclasts. 



Neumann and Bizzozero have advanced the opinion (Centratblatt, 

 1868, pp. 689, 855, and 1869, p. 149), that on account of the pre- 

 sence of nucleated red blood corpuscles, similar to those of the embryo, 

 red marrow is to be regarded as a blood gland. We have entirely 

 failed to find such corpuscles ; but, on the other hand, one can some- 

 times see a group of red corpuscles enveloped in a mass of clear colour- 

 less colloid material, similar to the bodies found in the spleen, and 

 which are there regarded as evidence of the disintegration of red cor- 

 puscles. 



TOOTH. 



130. Sections of unsoftened tooth are prepared accord- 

 ing to the same method as bone ( 118). Owing to the 

 absence of fat from the tooth pulp, however, the maceration 

 is soon accomplished. The method for softening tooth is 

 the same as that adopted for bone ( 119). The enamel, 

 however, disappears, owing to its very large percentage of 

 calcareous matter. 



131. Structure of Unsoftened Tooth. V. S. Unsoft- 

 ened Tooth. (L.) Observe the pulp cavity, the dentine, 

 the enamel outside the dentine in the crown, and the crusta 

 petrosa outside the dentine in the fang of the tooth. The 



