98 Animal Microloyy 



and shake the mixture vigorously until the blood becomes laky. Place 

 a drop or two of the laked blood on a slide and allow it to dry in the 

 cold. 



2) Hematoidin Crystals; reddish-yellow crystals (rhombic plates). 

 They can be obtained from old blood extravasations (e. g., cerebral hem- 

 orrhage, corpora lutea, etc.) by teasing. Mount in Canada balsam. 



3) Hemin or Teichmann's Crystals. To a small drop of blood on a slide 

 or a bit of cloth which has been previously saturated with blood, add a 

 few crystals of common salt. Heat over a flame until the mixture has 

 become dry, leaving a reddish-brown residue. Apply a cover-glass and 

 flood the preparation with as much acetic acid as will remain in place 

 under the cover. Heat the preparation until the acetic acid boils. After 

 the acid has evaporated the preparation may be made permanent by 

 adding Canada balsam. The crystals are very small, narrow rhombic 

 plates of dark brown color. They vary in size and may lie singly, across 

 one another, or in stellate groups. 



The presence of these crystals is positive evidence of the presence of 

 blood, hence their demonstration is of great importance in stains or fluid 

 suspected of containing blood. 



II. COVER-GLASS PREPARATIONS 



a) Dry preparations (Ehrlich's method). 1. In this method the 

 preparation is "fixed" by means of heat. Under one end of a copper 

 bar or copper triangle (Fig. 26) place a flame. After 15 or 20 minutes a 

 given point on the bar will have a practically constant temperature. 

 Thoroughly clean the bar, run a stream of water along the top of it 

 toward the flame, and locate the point farthest from the flame at which 

 the water boils. The blood smears when prepared are to be placed film 

 side up in a row across the bar about three-fourths of an inch nearer the 

 flame than the point at which the water just boiled. This will subject 

 them to a temperature of about 120 C. 



2. Thoroughly clean and dry two cover-glasses, touch one to a drop 

 of perfectly fresh blood as it comes from the finger or lobe of the ear and 

 instantly drop it onto the second cover. The blood should spread in a 

 thin film between the covers; if it does not, it has begun to coagulate 

 and the preparation will be inferior. Rapidly separate the covers by 

 sliding them apart, wave them in the air a minute to dry the films, tht-n 

 place them down with the smear side uppermost. Do not press the 

 covers together to spread the blood because this ruins the corpuscles. If 

 the red corpuscles are to retain their shape the film of blood must be 

 extremely and uniformly thin. Practice until you have prepared such 

 a film. 



