188 



BLOOD AND BLOOD-FORMING ORGANS. 



in the squirrel, however, in hexagonal plates, and in the guinea-pig 

 in tetrahedra. Hematin combines with hydrochloric acid to form 

 hemin, or Teichmanris crystals, of brownish color, rhombic shape, 

 and microscopic size. They are of much value in lego-medical 

 work, since they may be obtained from blood, no matter how old, 

 and are characteristic of hemoglobin. They may be obtained 

 from very small quantities of blood pigment. 



If .a small drop of blood pressed from a small puncture is 

 placed on a slide and covered with a cover-glass, the red blood- 

 cells soon become changed. This is due to the evaporation of 

 water in the blood plasma, causing an increased concentration of 

 the sodium chloride contained, which in turn draws water from the 

 blood-cells The shrinkage which follows produces a characteristic 



Fig. 151. Hu- 

 man red blood-cells ; 

 X 1500: a, As seen 

 from the surface ; l>, 

 as seen from the edge. 



v\W> 



Fig. 1-52. So-called 

 "rouleau" formation of 

 Jiuman erythrocytes ; X 

 1500. 



Fig. 153. Hemin, or 

 Teichmann's crystals, from 

 blood stains on a cloth. 



Fig. 154. "Crenated" human red blood- 

 cells ; X I 5- 



Fig- '55- Red blood-corpuscles sub- 

 jected to the action of water; X 1 S CO ' a > 

 Spheric blood-cell ; b, "blood shadow." 



change in the form of the cells, which assume a crenated or stellate 

 shape. The red blood-cells of blood mounted in normal salt 

 become crenated in a short time for the same reason. Red blood- 

 cells are variously affected by different fluids. In water they become 

 spheric and lose their hemoglobin by solution. Their remains then 

 appear as clear, spheric, indistinct blood shadows, which may, how- 

 ever, be again rendered distinct by staining with iodin. Dilute 

 acetic acid has a similar but more rapid action, with this peculiarity, 

 that before becoming paler the blood-cells momentarily assume a 

 darker hue. Bile, even when taken from the animal furnishing the 

 blood, exerts a peculiar influence upon the red blood-cells ; they 

 first become distended, and then suddenly appear to explode into 



