by marrow cells are found in the spaces between the trabec- 

 ulse (the primary marrow spaces). The} periosteal bone is 

 being formed, and is well marked off from the endochon- 

 dral bone. Sketch under low power, showing in your draw- 

 ing the several areas mentioned above. 



(c) Red Marrow. 



A small portion of red marrow taken from the femur 

 of a guinea pig was placed on a cover glass and covered by 

 another cover glass ; the two were then pressed together 

 and quickly drawn apart. They were then hardened for 

 24 hours in a solution of three parts ether and one of abso- 

 lute alcohol, and stained in haematoxylin and eosin. 

 Mount in balsam. 



Study under high power. Find and sketch the follow- 

 ing cells : 



(1) Mononuclear giant cell. 



(2) Polynuclear giant cell; the nucleus may be lobu- 

 lated, s-shaped, or in the form of a ring. 



(3) Nucleated red corpuscle; the spherical nucleus 

 takes the stain very freely. 



(4) Erythroblasts ; a little larger than the red blood 

 cells, and containing none or very little haemoglobin. 



(5) Polynuclear, transitional, and mononuclear white 

 blood cells, and perhaps a few lymphocytes. 



(6) Myelocytes or red marrow cells, mononuclear and 

 a little larger than the white blood cells. 



