CHAPTER XIV 

 BLOOD 



I. EXAMINATION OF FRESH BLOOD 



a) General. 1. Thoroughly clean a slide and cover, bathe a finger 

 in ether-alcohol (reagent 16, Appendix B), sterilize a sharp needle by 

 heating it in a flame and then prick the finger with the needle. 



2. Place a small drop of the resulting blood on a slide and quickly 

 put on a cover-glass. To prevent evaporation, the edges of the cover 

 may be surrounded by olive oil or vaselin. 



Living corpuscles may also be studied in a drop of normal saline. 



b) Effects of reagents. When it is desired to study the effects of 

 reagents on fresh blood (e. g., distilled water, 1 per cent, tannic acid, etc.) 

 a drop of fresh blood is placed on a jslide, the cover is put on and then 

 the blood is " irrigated " with the reagent. That is, a drop of the reagent 

 is placed at the edge of the cover to be drawn under by capillary action. 

 The process may be hastened by applying the edge of a bit of blotting 

 paper to the opposite edge of the cover. 



c) To demonstrate blood- platelets. Place a small drop of a 1 per 

 cent, solution of methyl violet (reagent 57, Appendix B) in normal salt 

 solution, on a finger which has been cleaned by washing it in ether- 

 alcohol. With a sterilized needle prick the finger through the stain and 

 mount a drop of the blood which exudes. Examine it under a high 

 power. Both platelets and white corpuscles are stained. 



d) Stained preparation of fibrin. Mount a drop of blood on a slide 

 as in a. Place it in a moist chamber for from 20 to 30 minutes to 

 coagulate. Loosen the cover with a few drops of water and then thor- 

 oughly irrigate the preparation with water. Drain off the water, blot 

 the preparation with blotting paper and add immediately a drop of a 1 

 per cent, aqueous solution of eosin (reagent 40, Appendix B). Remove 

 this after 3 minutes, rinse the preparation in water, then treat it 3 min- 

 utes with a 1 per cent, aqueous solution of methyl violet (reagent 57, 

 Appendix B). Rinse the preparation in water, let it dry, and finally 

 mount in balsam.' 



e) Crystals of the blood. 



1) Hemoglobin Crystals. Allow a drop of blood to dry on the slide 

 without covering it. Long rhombic prisms of a red color crystallize out. 

 The blood of a rat is best for demonstration. A more certain method is 

 as follows: To 5 c.c. of blood in a test-tube add a few drops of ether 



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