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 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. For comparison, 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 lamellae, 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. 



