VII PRACTICAL. DIRECTION 125 



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

 the bundles of white connective-tissue fibres, and the elastic fibres. 

 (Fig. 33). Sketch. 



Add acetic acid : the white fibres will be dissolved, the elastic fibres 

 more readily distinguished, and the connective-tissue cells seen ; the latter 

 and the delicate ground-substance will be rendered more distinct by 

 staining with methyl-green. Sketch. 



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

 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 cell- 

 spaces or lacuna, in each of which is a nucleated cell : observe here 

 and there the groups of cells formed by binary fission (Fig. 34). Stain 

 as before. Sketch. 



9- Bone. — For the examination of dried bone cut a very thin slice of 

 one of the dried long bones with a fret-saw : fasten it to a slide with 

 Canada balsam, 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, owing to their being 

 filled eithei* with air, or with bone-dust produced in grinding the section 

 (Fig. 35). A section of human bone, such as is usually supplied ready 

 prepared, or of the bone of some other lai-ger animal, shows a more 

 complicated structure : instead of a single system of lamellse, 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,^ and notice — the 

 fibrous lamella arranged in two layers, the outer of which is closely 

 invested by the periosteum ; the cell-spaces or lacuna, containing bone- 

 cells ; and the outer and inner layers of osteoblasts (Fig. 36). Sketch. 



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



' The method of preparing sections of this and other tissues will be 

 described at the end of the next chapter. 



