9 o 



THE MICROSCOPE. 



central cavity, and like it are filled with marrow. By 

 examining a transverse section of a long bone you 

 will see that the small orifices of the canals are in the 

 centre of the layer forming the bone, which is arranged 

 round them in concentric rings ; between these layers 

 are small open spaces called lacuna. They are cavi- 

 ties from which the canaliculi extremely minute 

 spider-like tubules, which perforate the bony layers and 

 communicate with the central Haversian canal pro- 

 ceed. Blood-vessels, from the membrane surrounding 

 the bone termed the periosteum, are traceable intQ the 

 Haversian canals. The canaliculi are too small to 

 allow the admission of blood-corpuscles. I may here 

 mention the effect of madder, when given to- an animal 

 in its food, upon the osseous system. The bones 

 become coloured with a 

 deep red tinge. The bones 

 of a pigeon were rendered 

 red in about twenty-four 

 hours ; it took three weeks 

 to colour the bones of a 

 young pig. Both the external 

 and internal laminae of the 

 bone are found to be affected 

 by the colouring matter, 

 proving thereby that the 

 action takes place on those 

 parts which lie in contact 

 with blood-vessels. 



You will be interested to 

 hear that an intimate know- 

 ledge of the structure of bone, as acquired by 

 the aid of the microscope, has proved of immense 

 value in determining the tribe of animals to which 

 bones belonged. I shall quote Dr. Carpenter's graphic 

 words : " From the average size and form of the 



Section of Humerus of Turtle. 



