GENERAL PROPERTIES! THE CORPUSCLES. 419 



than in the case of the leucocytes.* When removed from the circu- 

 lating blood they are known to disintegrate very rapidly. This 

 peculiarity, in fact, prevented them from being discovered for a long 

 time after the blood had been studied microscopically. It has been 

 shown that they are formed elements, and not simply precipitates 

 from the plasma, as was suggested at one time. The theory of 

 Hay em, their real discoverer, that they develop into red corpuscles 

 may also be considered as ' erroneous. There is considerable evi- 

 dence to show that in shed blood they take part in the process of 

 coagulation. The nature of this evidence will be described later. 

 On account of their small size and somewhat indefinite form the 

 structure of the blood plates is not satisfactorily known. Deetjenf 

 has demonstrated that they are capable of ameboid movements. 

 When removed from the blood vessels to a glass slide they usually 

 agglutinate into larger or smaller masses, swell, and disintegrate, 

 but if received upon a surface of agar-agar which has been made up 

 with physiological saline, together with some sodium metaphos- 

 phate (NaPO 3 ), they flatten out, show a central granular portion 

 and a peripheral clear layer, and may make quite active ameboid 

 movements. Deetjen claims also that they possess a distinct 

 nucleus. This latter statement is perhaps doubtful, as other 

 observers report that the material which stains like a nucleus is 

 present as separate granules in the interior of the plate. These 

 granules, though doubtless of nuclear material, do not have the 

 morphological appearance of a cell nucleus. It remains, therefore, 

 uncertain whether the blood plates are to be considered as inde- 

 pendent cells or as fragments of disintegrated cells. On account 

 of their tendency to agglutinate and dissolve when the blood is shed 

 it is difficult to obtain reliable data as to their numbers under 

 normal and pathological conditions.! The results obtained by 

 later observers using special methods to prevent known sources of 

 error indicate that the average number may be 500,000 per cubic 

 millimeter. The extremes reported vary from 200,000 or 250,000 

 to 778,000. Under certain pathological conditions, especially in 

 pernicious anemia and lymphatic leukemia, their number is greatly 

 reduced. Outside the part that they take in the formation of 

 thrombi and in the initiation of coagulation, nothing is known 

 of their function under normal conditions. 



* Wright ("Boston Medical and Surgical Journal," June 7, 1906) 

 calls attention to a relationship between the blood plates and the giant cells 

 of the marrow (megalokaryocytes), and ventures the opinion that the 

 plates are detached pieces of the cytoplasm of the giant cells. 



t "Virchow's Archiv f. path. Anat. u. Physiol.," 164, 239, 1901. 



J For a summary of the literature and methods consult Kemp, "Journal 

 of the American Medical Association, " April 7 and 14, 1906, and Pratt, ibid.l 

 Dec. 30, 1905. The preservative solution recommended by Pratt consists 

 of sodium metaphosphate, 2 grams; sodium chlorid, 0.9 gram; water, 100 c.c. 

 That preferred by Kemp is, formalin (40 per cent., aqueous solution of for- 

 maldehyd), 10 c.c.; sodium chlorid (1 per cent, solution), 150 c.c. 



