SUGGESTIONS FOR LABORATORY WORK 607 



two clean microscopic slides. Congest the blood in the middle 

 finger of the left hand by wrapping a handkerchief tightly about 

 it, beginning at the base. Prick the congested region sharply with 

 a clean needle and squeeze out a drop of blood. Bring the surface 

 of one of the slides near one end in contact with the drop of blood. 

 The blood will adhere to the slide. Quickly place an edge of the 

 second slide against the surface of the first one and move it along 

 till it comes in contact with the blood-drop. The latter should 

 spread out along the edge of the second slide. Now draw this 

 slide along the first one. The blood will follow, and thus be spread 

 out in a thin layer. Let the slide dry for a few minutes before be- 

 ginning observations. No cover glass is needed, but the slide 

 should be kept free from dust. 



Place the prepared slide on the stage of the microscope and focus 

 on it with the low power. Numerous pale yellow specks will be 

 seen. These are red corpuscles. Some idea of their great numbers 

 in the blood can be gained by comparing the area of the field of the 

 microscope with that over which the original blood-drop was 

 spread, and that drop, in turn, with the whole volume of blood 

 in the body. 



Change from the low-power objective to the high power. Note 

 that by this change the field is much reduced. After obtaining a 

 sharp image, study individual red corpuscles carefully. Compare 

 the margin of a corpuscle with its center. The different appearance 

 of the two regions signifies that the corpuscle is a disk thicker at 

 the edges than in the center. 



Look for groups of corpuscles arranged in rows, edge to edge. 

 These are rouleaux. Corpuscles in shed blood tend to cling together 

 thus. 



By exploring the slide carefully, colorless corpuscles can be found 

 and studied. They are transparent, colorless bodies about twice 

 the diameter of red corpuscles. They are much less numerous than 

 red corpuscles. The ratio is about 1 to 300. 



The various kinds of colorless corpuscles can be distinguished 

 by their appearance after treatment with suitable stains. On pre- 

 pared slides different types of colorless corpuscles can be studied. 



Chemical Structure. Blood plasma * is an exceedingly complex 



*The liquid part of clotted blood is called serum. That of unclotted 

 blood is called plasma. 



