208 



THE BLOOD 



are scarcely half as large as the red corpuscles, but cells considerably 

 larger or smaller than these are not uncommon. Their number is 

 usually given as 180,000 to 800,000 per cu. mm., which means that they 

 are more numerous than the leukocytes. 



Methods of Examination. — A few platelets can always be secured 

 by carefully collecting a drop of blood in normal saline solution; much 

 better results, however, are obtained with Haymen's fluid. ^ Bizzozero^ 

 recomniends a solution of 30 per cent, gentian violet in a 0.75 per cent, 

 sodium chlorid solution. Their immediate fixation may be achieved 

 by drawing the blood into a 1 per cent, solution of osmic acid, or better 

 still, by previously moistening the tip of the finger from which the 

 blood is to be taken with this solution.^ Deetjen preserves them by 

 permitting a droplet of blood to flow upon agar jelly. ^ By making use 



of their slight specific gravity, Biirker^ sepa- 

 rates them from the other formed elements in 

 the following manner. A drop of blood is 

 collected upon a thin sheet of paraffin and is 

 allowed to stand for a short time. The lighter 

 platelets collect near the surface of the drop 

 and may be removed by drawing a cover-glass 

 through its upper layers. 



Origin and Fate of the Blood Platelets. — 

 Haymen, their discoverer, regarded the throm- 

 bocytes as carriers of hemoglobin and there- 

 fore as transitional types of the red corpuscles. 

 He designated them as hematoblasts. Bizzo- 

 zero, on the other hand, first expressed the 

 view that they are independent elements and 

 are therefore neither embryonic red cells nor the remnants of destroyed 

 corpuscles. To be sure, fragmented red cells may'appear in the blood 

 at times, but a differentiation between these bodies and the blood 

 platelets, as described by Bizzozero, is readily possible upon the basis 

 of their histological characteristics. The supposition that the throm- 

 bocytes are fragmentary white corpuscles also lacks satisfactory con- 

 firmation. Thus, it is a well-known fact that the latter do not dis- 

 integrate in great numbers in the circulating blood and neither do 

 they break up with undue rapidity in shed blood. It may indeed 

 be concluded that they are relatively resistant, because they are often 

 preserved in extra vascular and intravascular coagula of long standing. 

 The conclusion, that the thrombocytes are not derived from the 



1 Archives de physiol. norm, et pathol., x, 1878. 



2 Virchow's Arch, fur path. Anat., xc, 1882. 



3 Kemp, Stud., Biol. Lab., J. Hopkins Univ., iii, 1886. 



^ Made by dissolving 5 gr. of agar-agar in 500 c.c. of distilled water. To 100 

 c.c. of the filtrate are added 0.6 gr. NaCl solution, 6 to 8 c.c. of a 10 per cent. 

 NaPOa solution and 5 c.c. of a 10 per cent. K2HPO4 solution. See: Deetjen, Vir- 

 chow's Archiv, clxiv, 1901, 260. 



^ Pfluger's Archiv, cii, 1904, 36. 



Fig. 113. — Thrombocytes 

 Highly Magnified. 



