vii PRACTICAL DIRECTIONS 125 



Examine first with the low and then with the high power, 

 and note the bundles of white fibres, and the elastic fibres 

 (Fig. 33). Sketch. 



Add acetic acid : the white fibres will swell up, the elastic 

 fibres are more readily distinguished, and the connective- 

 tissue cells seen : the latter and the delicate ground -substance 

 will be rendered more distinct by staining. (For comparison 

 with this areolar tissue, mount in salt solution a piece of one 

 of the fine tendons of the toes : treat as before, and 

 examine.) Sketch. 



8. Cartilage. Snip off the thin edge of the omo- or xiphi- 

 sternum or supra-scapula and examine it as before in a drop 

 of salt-solution. Or, cut a thin section of the head of the 

 humerus or femur with a razor. 



Note the transparent, homogeneous matrix, containing 

 numerous lacuna, in each of which is a nucleated cell : 

 observe here and there the groups of cells formed by binary 

 fission (Fig. 34). Stain, and sketch. 



9. Bone. For the examination of dried bone, cut a very 

 thin slice of one of the long bones with a fret-saw : fasten it 

 to a slide with Canada balsam (p. 136), and when the balsam 

 has dried quite hard, rub down the section on a hone until 

 it is thin enough to be quite transparent. Or, a transverse 

 section of a bone from a larger animal may be prepared in 

 the same way or bought from a dealer in microscopic objects. 



a. Examine first a transverse section of dry frog's bone 

 (e.g. femur or humerus), and note the marrow-cavity, the 

 lamella, and the lacuna and canaliculi ; the two last will 

 probably appear black (p. 117 and Fig. 35). A section of 

 human bone, such as is usually supplied ready prepared, or 

 of the bone of some other larger animal, shows a more 

 complicated structure : instead of a single system of la- 

 mellae, the bone consists of a number of such systems, each 

 surrounding a central canal, in which blood-vessels and 

 nerves run, and which corresponds to the marrow-cavity in 

 the simpler frog's bone described above. Sketch. 



b. Compare with a section of decalcified frog's bone, 1 and 

 notice the fibrous lamella arranged in two layers, the outer 

 of which is closely invested by the periosteum ; the lacuna, 

 containing bone-cells ; and the outer and inner layers of 

 osteoblasts (Fig. 36). Sketch. 



(For the histology of nervous tissue, see Chapter X.) 



1 The method of preparing sections of this and other tissues 

 will be described at the end of the next chapter (p. 136). 



