38 THE FROG 



the leucocytes and lymphocytes, are much less numerous and very 

 transparent; they are much smaller than the red cells. Some of them 

 will be seen to be irregular in shape and you may possibly see that 

 some of them change shape while you watch them. Their nuclei can- 

 not be recognized. Make drawings of red blood cells in different 

 positions, to show their shape. Make drawings of the white blood cells. 

 These drawings are to be 3 X the measured size of cells as projected 

 to table level. Record total magnification and source of tissue. 



(j) Stain a fresh preparation with methyl violet by placing a 

 small drop of the stain at the edge of the cover glass and allowing 

 it to run under. Study especially the white blood cells in which the 

 nuclei are now visible, and add to your drawing. 



(k) Examine again the circulation of blood in the web of the frog's 

 foot, looking for the two kinds of corpuscles and noting the relative 

 size of the blood cells and the capillaries. 



(1) Examine demonstrations of fresh and stained human blood. 

 Compare with frog's blood with respect to size and shape of the red 

 blood cells. Do you find nuclei? Do the white blood cells seem to 

 differ in number or appearance from those of the frog? Observe, in 

 a demonstration of undiluted blood, that the red blood cells may be 

 arranged in rows like piles of coins. These are called rouleaux. 



Exercise 35. — Non-striated Muscle. 



(m) Obtain, in a drop of liquid, a piece of the digestive tract of 

 the frog which has been macerated. Tease thoroughly and add a 

 cover glass. Study first with the low-power objective and then with 

 the high -power objective. The cells are elongated and taper toward 

 their ends, and each has a prominent nucleus near the middle. 

 Measure the length of a cell as projected to table level and draw 

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

 of the tissue. 



Exercise 36. — Striated Muscle. 



(n) Obtain a small bit of muscle from a freshly killed frog and 

 place it at once in a clean watch glass half full of 0.7% salt (sodium 

 chloride) solution, or Ringer's solution. Do not at any time give the 

 material the least chance to dry. Fray out the piece with needles, 

 separating but not injuring the individual fibers which you can see. 

 Mount a few fibers on a slide in salt solution without staining. Also, 

 stain a small mass of fibers as follows: put a drop of methyl violet 

 on one end of a slide and a drop of water on the other; with forceps, 

 put several fibers into the stain and leave them for about a minute; 



