33 

 LESSON IX. 



BONE. 



(a) Cross-Section of Bone. 



From a thoroughly macerated and dried bone a thin cross- 

 section is removed from the shaft by means of a fine saw. This is 

 ground between two hones until it becomes very thin and trans- 

 parent, care being taken to keep the stones well moistened with 

 water, and not to use too much pressure. The section is now 

 washed, first in distilled water, and then in alcohol. This is best 

 done by means of a fine camel's-hair brush, using a deep watch 

 crystal. In order to determine whether your section is clean, 

 mount it in a drop of alcohol, and examine under the microscope. 

 The Haversian canals and the lacunae must be free from sand, as 

 they will be if the section is well washed. If clean, dry between 

 two filter papers. A dry bone section must be mounted in hard 

 balsam. To prepare this, place a large drop of balsam on a slide, 

 and another on a cover glass. Heat both over the flame for a few 

 moments, and then set aside to cool. When ready the touch of a 

 needle will make a dimple in the balsam. Then place the bone 

 section on the balsam and cover with the prepared cover slip. 

 Gently press the cover with a needle until the layers of balsam fuse. 



Examine under low power. Observe that in a Haver- 

 sian system the bone lamellae are concentrically arranged 

 about the Haversian canal. Note the bone lacunaa between 

 the lamellae ; these communicate with one another by 

 means of the fine canaliculi. Look for the interstitial and 

 circumferential lamellas. Sketch several Haversian sys- 

 tems as seen under low power. 



(b) Longitudinal Section of Bone. 



A thin longitudinal section is made from the shaft of a bone by 

 means of a fine saw. Grind and wash as above. Dry and mount in 

 hard balsam. 



