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 1 and Welker 2 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- 



D 



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. 3 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, fur physiol. Heilkunde, xiii, 1854, 259. 



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



3 See Abb4: Sitzungb. d. 'Jenaischen Gesellsch. f. Med., 1878; also see: Burker, 

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

 Untersuchungsmethoden, Leipzig, 1909. 



