BLOOD FLOW 



39 



BLOOD PLATELETS 



9.9 cc. saline in photoelectric colorimeter 

 tube. Make blank without plasma. 

 Compare in Evelyn or Klet-Summerson 

 colorimeter using filter to pass only light 

 of about 620 m/x. Calculate as directed 

 for the colorimeter (Shohl, A. T. and 

 Hunter, T. H., J. Lab. & Clin. Med., 

 1941, 26, 1829-1837). See also earlier 

 cell opacity method (Shohl, A. T., J. 

 Lab. & Clin. Med., 1939-40, 25, 1325- 

 1332). 



Blood Flow, technique for local measure- 

 ment of, using radioactive sodium 

 (Semple, R., McDonald, L. and Ekins, 

 R. P., Am. Heart J., 1951, 41, 803-809). 



Blood Grouping technique does not properly 

 come in the scope of this book; but since 

 it is involved in fundamental medical 

 and biological problems the following 

 leading reference is given: Schiff, F., 

 and Boyd, W. C, Blood Grouping 

 Technic. New York: Interscience Pub- 

 lishers, Inc., 1942, 248 pp. 



Blood Platelets— Written by Paul M. Ag- 

 geler, University of California Medical 

 Center, San Francisco 22, California. 

 November 15, 1951 — It is believed by 

 most authorities today that the plate- 

 lets originate from megakaryocytes, 

 chiefly in the bone marrow but perhaps 

 also in the lungs. The platelets are 

 thought to be detached fragments of the 

 cytoplasm of mature megakaryocytes. 

 In man the platelets usually vary be- 

 tween 2 and 3 microns in length, al- 

 though microplatelets of less than one 

 micron and macroplatelets as long as 25 

 to 50 microns have been observed. 

 They vary in thickness from 0.5 to 1.0 

 micron. In rapidly fixed blood they 

 usually assume the shape of an oval disc 

 or lentil although a variety of forms 

 may be encountered. In unfixed blood, 

 even in the presence of an isotonic 

 anticoagulant many degenerative forms 

 may occur. These may appear shrunken 

 or "exploded" and there may be numer- 

 ous spinelike projections from the sur- 

 face of the platelet. In dry smears of 

 imperfectly fixed blood stained with 

 Wright's stain the platelets appear to 

 be divided into two zones: the clear 

 blue hyalomere and the chromomere 

 made up of purple staining granules. 

 This separation into two zones is prob- 

 ably an artefact produced by changes 

 in distribution of the granular material 

 of the platelet after leaving the circula- 

 tion, for when blood is rapidly fixed 

 the granules are evenly distributed 

 through the body of the platelet. 

 Macroplatelets found in the blood in 

 periods of abnormal blood regeneration 

 often take a deeper stain and the 

 granules are coarse and do not show, 

 even in slowly dried preparations, the 



clear separation between hyalomere 

 and chromomere. 



Platelets are found in the circulating 

 blood, particularly in the capillaries of 

 the liver and lung, in the bone marrow 

 and in the spleen, both in the sinuses 

 and between the cells of the pulp. 

 They are not found in the lymph or in 

 the thoracic duct. More platelets are 

 found in arterial than in venous or 

 capillary blood. 



Physiological decreases in the plate- 

 let count are said to occur during the 

 first day of menstruation and increases 

 have been found after violent exercise 

 and following a change to a high alti- 

 tude. An increased platelet count 

 (thrombocytosis) may be found in in- 

 fectious diseases, trauma, fractures, 

 asphyxiation, surgical operations, acute 

 blood loss, chronic myelocytic leu- 

 kemia, Hodgkin's disease and erythre- 

 mia. A decreased platelet count 

 (thrombocytopenia) is the basic defect 

 in idiopathic thrombocytopenic purpura 

 and also occurs secondarily in certain 

 acute infectious diseases of the blood 

 and blood forming organs, diseases of 

 the spleen, allergies, sensitization reac- 

 tions to certain drugs and chemicals, 

 and following the use of certain toxic 

 agents such as benzol or ionizing radia- 

 tions. 



The platelets are thought to survive 

 in the circulation of the normal subject 

 for from three to five days. There is 

 recent evidence to suggest that in 

 idiopathic thrombocytopenic purpura 

 they are destroyed at a much more 

 rapid rate. The reduction of the plate- 

 let count in this disease had previously 

 been thought to be due either to failure 

 of production of the platelets or to 

 abnormally rapid removal from the 

 circulation by phagocytosis in the 

 spleen. The mechanism of reduction 

 of the platelet count in secondary 

 thrombocytopenic purpuras may be: 

 (1) destruction of megakaryocytes as 

 in ionizing radiation; (2) splenic in- 

 hibition of maturation of megakaryo- 

 cytes as in congestive splenomegaly or; 

 (3) a direct inhibition of maturation 

 of megakaryocj'tes as in sensitivity 

 reactions to drugs. 



The platelets are concerned in the 

 coagulation of the blood, in retraction 

 of the blood clot, in the formation of 

 thrombi and in the maintenance of 

 capillary continuity. The most signifi- 

 cant property of platelets is the readi- 

 ness with which they agglutinate in 

 shed blood or when exposed to a for- 

 eign surface. Agglutination is gener- 

 ally followed by fusion and lysis. 



Direct Methods: The principle of all 



