00 



Lesson IX. 



BONE. 



(a) Cross-Section of Bone. 



Fi-uiii ii tlioruuglily inarcratod and dricil bone a tliiii cross- 

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

 ground l)et\veen two iiones until it l)ec;onies very tliin 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 alcoliol. This is best 

 done Ijy means of a line camers-hair brush, using a deep watch 

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

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

 Tiie Haversian canals and tlie lacuiiie 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 prc]>are this, place a large drop of balsam on a slide, 

 and another on a cover glass. Heat l)oth over the flame for a few 

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

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

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

 C-iently press the cover with a needle until the layers of balsam fuse. 



Examine under low power. Observe that in a Haver- 

 sian system tlie bone lamellae are concentrically arranged 

 about the Haversian canal. Note the bone lacunse between 

 the lamellse; these communicate with one another by 

 means of the fine canaliculi. Look for the interstitial and 

 circumferential laiuellfe. 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 aljove. Dry and mount in 

 hard balsam. 



