446 BLOOD AND LYMPH. 



smaller than the red corpuscles. 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 the structure of the blood plates 

 is not satisfactorily known. Deetjen* 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 metaphosphate (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 possibly 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 independent cells or as fragments 

 of cells. The origin or histogenesis of the plates has been studied 

 by many observers. Numerous 'hypotheses have been suggested; 

 that they originate from the nuclei of the polynuclear leucocytes; 

 that they are extruded remnants of the nuclei of the young red 

 blood-corpuscles; that they are detached pieces of the cytoplasm 

 of the giant cells (megakaryocytes) of the bone-marrow, etc., but 

 no one of the hypotheses proposed has found general acceptance. 

 The origin, fate and function of these interesting bodies are still 

 open questions in spite of the great amount of investigation de- 

 voted to the subject. The normal number of the plates in the 

 circulating blood is large, but the estimates made vary somewhat 

 with the method used.f When the blood is shed the plates 



* "Virchow's r Archiv f. path. Anat. u. Physiol.," 164, 239, 1901, also 

 Zeitschrift f. physiol. chemie, 63/1, 1909. 



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

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

 Dec. 30, 1905, and Wright and Kinnicutt, "Transactions of Assoc. of Am. 

 Physicians," May, 1901. 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 formaldehyd), 10 c.c.; sodium chlorid (1 per cent, solution), 150 c.c., while 

 Wright employs a solution of cresyl blue and potassium cyanid. 



