THE MICROSCOPE. 49 
after which they are placed for 24 hours in a liberal quantity of 
chloroform. 
Now take a quantity of Canada balsam and heat it over a 
water-bath not higher than 90° F., until the mass when cold will 
eratk like glass when broken. Make a thin solution of this with 
chloroform and immerse the specimens in it for 24 hours. Now, 
without removing the specimens, add as much more balsam as the 
chloroform will dissolve, when they are again put over the water- 
bath, covered with a sufficient quantity of the thickened solution, 
until the glass-like mass has been reformed. They can now be 
thinned down on a stone and polished in the usual way, care being 
taken to wet them frequently with cold water during the operation, 
in order to prevent overheating. They are to be mounted in chloro- 
form balsam. 
This last method, though somewhat more tedious, will give by 
far the best results and is recommended to those who have the 
patience to go through with it. 
Examine a cross section with a low power. A number of con- 
centric rings will be seen around an open center. The markings of 
the rings are spaces between layers or /amelle of bone tissue 
and the open center represents an Haversian canal. Hach group 
of concentric lamelle, with the inclosed Haversian canal, is called an 
Haversian system. Looking more closely, it will be seen that all of 
the lamellz do not contribute to the formation of an Haversian sys- 
tem, but that many of them are tucked in between the various 
systems, whilst others run parallel with the surface of the bone. 
This has given rise to a classification of lamellze into (1) concentric 
lamellzxe (those forming a Haversian system); (2) peripheric or 
interstitial lamellze (those tucked in between the systems); and (3) 
intermediate or circumferential lamellz (those running parallel with 
the surface of the bone). The lamellee are composed of fine bundles 
of fibrous tissue impregnated with lime salts, 
Between the lamellz will be seen a number of dark spots rep- 
resenting spaces called lacune, and, with a higher power, from these 
a number of delicate channels radiating in all directions, called 
canaliculi. The canaliculi running from one lacuna anastomose 
with those from neighboring lacunz, not only of the same sys- 
tem, but with others as well. Lacune near the surface communicate 
in this manner with the periosteum and those nearest the Haversian 
canals send prolongations into them. It will thus be seen that bone is 
very vascular. 
