1 2 Physiology. 



The Skeleton of a Cat or Rabbit. Examine the skeleton of a cat or 

 rabbit for the sake of comparison. Note especially the skull and spinal 

 column. This knowledge will aid in understanding the brain and 

 spinal cord. 



The Weight of Bones. The bones make about one sixth 

 of the weight of the living body. When dried they may 

 lose half of their weight. 



Microscopic Structure of Bone. i. Examine with a Hand Lens. 

 Hold a mounted cross-section of bone up to the light and examine with 

 a hand lens. The solid part of the bone will be seen to be pierced by 

 many small holes (or if the holes are filled, they will appear as black 

 spots). These are the cross-sections of the canals, through which run 

 the blood tubes, mainly lengthwise, through the bone. 



2. Examine with the Low Power of a Compound Microscope. 

 Examine the section under the microscope, using a half-inch objective. 



The bony matter will now be seen to be arranged in rings around the 

 canals, somewhat like the rings seen on the end of a log. 



Between the rings are circles of elongated dark dots. These are 

 cavities in which were the live bone-corpuscles which built up the bone. 

 The bone was at first cartilage. Later, mineral matter was deposited, 

 forming true bone. 



3. Examine with a High Power. Now examine the section under a 

 one-fifth-inch objective. From the dark cavities there run out, in every 

 direction, little crevices, appearing as fine black lines. Through the 



fyjaversian canals, lacunas, and crevices} the nourishing materials of the 

 blood reach all parts of the bone. 



The Chemical Composition of Bone. i . Take a tall, narrow jar, or 

 a lamp chimney corked at one end, and nearly fill with water. Add 

 one sixth as much hydrochloric acid. Put into this a slender, dry bone, 

 such as a fibula or rib. In twenty-four hours take it out, rinse it thor- 

 oughly, and examine it. The acid will probably have dissolved out the 

 mineral matter and left the animal matter so soft that it may be tied 

 into a knot. 



2. Lay a piece of bone on a shovel, or piece of sheet iron, and place 

 in the fire. The animal matter is burned out, leaving the brittle min- 

 eral matter. 



