HISTOLOGY 37 



salt (sodium chloride) solution, or Ringer's solution. After locating 

 with the low-power objective the thinnest part of the section and 

 distinguishing the cartilage proper from the regions in which bone is 

 being formed, study with the high-power objective. Cartilage is a 

 tissue having its cells widely separated by a matrix of a semitrans- 

 parent, lifeless material. The cartilage cells lie in cavities, called 

 lacunae, surrounded by the matrix. In some lacunse there may be two 

 cells, or two lacunas may be seen close together with flattened adjacent 

 sides, indicating that cell division has recently taken place. Can you 

 also find cells in fours? Measure the diameter of a cell as projected 

 to table level. Make a drawing of this and several adjacent cells 

 (3 X the measured size). Record the total magnification and the 

 source of the tissue. 



Exercise 33. — Bone. 



(h) Pieces of dried bone, ground to thin sections, will be used. 

 In these sections only the inorganic substance of the bone remains, 

 but the extent and distribution of the bone cells are shown by the 

 cavities which the cells once occupied. These lacunae appear black 

 because in the grinding of the section they become filled with dirt 

 and air. Examination with the high-power objective will show the 

 lacunse as elongated, black areas which were formerly occupied by 

 cells and, radiating from them, fine black lines, the canaliculi, which 

 in life were occupied by delicate processes of the bone cells. Com- 

 pare the structure here observed with that seen in cartilage. In some 

 bones the cells are grouped about canals in which blood vessels run. 

 These are called Haversian canals, and each one, together with its 

 surrounding cells, constitutes a Haversian system. The bone cells 

 and their nuclei can be seen in stained sections of decalcified bone. 

 Examine, if available. Make a drawing (3 X measured size) of a 

 Haversian canal and some of its surrounding lacunse. Record total 

 magnification and source of material. 



Exercise 34. — Blood. 



(i) Place on a slide a drop of frog's blood slightly diluted with 

 0.7% salt (sodium chloride) solution, or Ringer's solution. Cover at 

 once, before it has time to dry, since drying changes the appearance 

 of the cells. Examine with the low-power objective. Blood is a tissue 

 composed of two kinds of cells, or corpuscles, suspended in a fluid, 

 the plasma. What is the color of the red blood cells, or erythrocytes, 

 as here observed? Determine their shape by observing them in dif- 

 ferent positions. The nucleus is readily seen. The white blood cells. 



