GENERAL PROPERTIES: THE CORPUSCLES. 443 



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 ex- 

 truded remnants of the nuclei of the young red blood-corpuscles; 

 that they are detached pieces of the cytoplasm of the giant cells 

 (megacaryocytes) of the bone-marrow, etc. No one of the hypoth- 

 eses proposed has found general acceptance, but an increasing 

 amount of evidence favors the last named theory. The megacary- 

 ocytes lie on or near the capillaries of the bone-marrow, and their 

 ameboid processes penetrate the walls of the capillaries and then 

 break up into plates, which are thus liberated in the blood-stream. 

 The fate and function of these interesting bodies are still open 

 questions in spite of the great amount of investigation devoted 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.* When the blood is shed the plates agglutinate 

 quickly into masses which soon disintegrate more or less com- 

 pletely. In dissolving they yield to the plasma material (pro- 

 thrombin and thromboplastic substance) which initiates the act 

 of clotting, as will be described in the next chapter. One function, 

 therefore, performed by the blood-plates is to ensure the coagula- 

 tion of extravasated blood. The average number of plates may be 

 given as 300,000 per cubic millimeter. The extremes reported 

 vary from 200,000 or 250,000 to 778,000. Under certain patho- 

 logical conditions, especially in pernicious anemia and lymphatic 

 leukemia, their number is greatly reduced, while in the acute 

 infectious diseases there is said to be a diminution in number 

 during the period of fever, followed by a marked increase beyond 

 the normal during the period of convalescence. A number of 

 observers have stated that in hemorrhagic diseases in which there 

 is delayed coagulation and tendency to bleed there may be a great 

 reduction in the number of platelets. Dukef states that in such 

 cases transfusion of blood from a normal person removes the hemor- 

 rhagic tendency, while increasing markedly the number of plate- 

 lets. But in three days the number of platelets again falls to a 

 low level, and simultaneously there is again a tendency to spon- 

 taneous bleeding. The observation is of interest as indicating 

 that the life history of the platelets in the circulation is probably 

 very brief. 



* 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 Amer. 

 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 cre.syl blue and potassium cyanid. 



t Duke, "Journal Amer. Med. Assoc," 55, p. 1185, 1910. 



