BONE AND MARROW. 57 



LESSON XIII. 



BONE AND MARROW. 



1. IN thin sections of hard bone made by grinding, observe the Haversian 

 canals, lamellae, lacunae, canaliculi, etc. Make a sketch first under a low and 

 afterwards under a high power. 



2. With fine forceps strip off a thin shred from the superficial layers of a 

 bone which has been decalcified in dilute nitric acid and afterwards kept for 

 some time in dilute alcohol. Mount the shred in water. Observe the fibrous 

 structure of the lamellae. Look for perforating fibres or the holes from 

 which they have been dragged out. Sketch a small piece of the thin edge of 

 a lamella. 



3. Stain with dilute magenta very thin sections of compact bone which 

 has been decalcified in chromic or picric acid, and mount in dilute glycerine, 

 cementing at once. Look for fibres of Sharpey piercing the circumferential 

 lamellae. The elastic perforating fibres are more darkly stained than the 

 others. Notice the stained nuclei of the bone-corpuscles in the lacunae. In 

 the thinnest parts of the sections try to make out the blood-vessels and other 

 structures in the Haversian canals. 



4. Mount in Canada balsam sections of marrow (from a long bone of a 

 rabbit) stained with haematoxylin. 1 Observe the fat-cells, the reticular 

 tissue supporting them, the proper marrow-cells in this tissue, etc. 



5. Tease in salt solution or serum some of the red marrow from the rib of a 

 recently killed animal. Observe and sketch the proper marrow-cells and 

 look for myeloplaxes and nucleated coloured blood-corpuscles. If examined 

 carefully, amoeboid movements may be detected in the latter and in the 

 marrow-cells. 



Bone is a connective tissue in which the ground-substance is im- 

 pregnated with salts of lime, chiefly phosphate, these salts constituting 

 about two-thirds of the weight of the bone. When bones are macerated 

 this earthy matter prevents the putrefaction of the animal matter. 

 When bones are calcined they lose one-third of their weight, owing to 

 the destruction of the animal matter ; when steeped in acid the earthy 

 salts are dissolved and only the animal matter is left. This, like 

 areolar and fibrous tissue, is converted into gelatine by boiling. 



Bony tissue is either compact or cancellated. Compact bone is dense 

 like ivory ; cancellated is spongy with obvious interstices. The outer 

 layers of all bones are compact, and the inner part is generally can- 



1 See Appendix. 



