176 



THE BLOOD 



altered, they are designated as poikilocytes. The latter usually 

 exhibit pointed projections, like burs, or surfaces beset with rounded 

 elevations. 



Number of the Red Blood Corpuscles. — While the method for the 

 counting of the red cells, devised by Vierordt^ and Welker^ has been 

 modified by different authors, the principle involved in it has remained 

 the same. The instrument most commonly used to-day is the hemo- 



\^ 



Fig. 102. — Hemocytometer. (Thoma-Zeiss.) 

 A, pipet; B, glass bead; C, counting chamber seen from side; D, counting chamber 

 seen from above; E, field as seen under microscope. 



cytometer of Thoma-Zeiss.^ It consists of a pipet (A), originally 

 devised by Potain, and a counting chamber (C). Having thoroughly 

 cleansed the skin upon the tip of the finger or upon the lobule of the ear, 

 a small wound is made with a lanzette or needle. A portion of the 

 blood collected upon the integument is then quickly drawn into the 



1 Arch, fiir physiol. Heilkunde, xiii, 1854, 259. 



^ Prager Viertalj. fiir prakt. Heilkunde, iv, 1854, 



2 See Abb6: Sitzungb. d. Jenaischen Gesellsch. f. Med., 1878; also see: Biirker, 

 Handworterb. der Naturw., Jena, 1912; and Hayem, in Sahli's Lehrb. d. klin. 

 Untersuchungsmethoden, Leipzig, 1909. 



