THE BLOOD-PLATELETS 75 



of Sauropsida and Ichthyopsida in our hands does not yield similar 

 bodies. The platelets figured by Osier within the vessels are 

 often reproduced as illustrations, but since they were only 

 occasionally observed in the excised venules in pieces of 

 subcutaneous tissue removed from the back of rats and spread 

 out on a slide, it is open to question whether this is convincing 

 evidence that they exist normally in blood. 



It is by no means certain that different authors who have 

 contributed to our knowledge of the platelets are really describing 

 the same things. The varied terminology which has been 

 employed also leads to some confusion. The name " Blut- 

 plattchen " we owe to Bizzozero ; the French School have 

 accepted Hayem's term, or haematoblast ; Eisen speaks of these 

 bodies as plasmocytes ; Dekhuyzen and Kopsch as thrombo- 

 cytes ; while the use of such names as endoglobular bodies 

 (Hirschfeld), true and false platelets, Arnold's bodies, Woold- 

 ridge's bodies, Deetjen's bodies, all of which, together with that 

 of microcytes (Pappenheim), have been employed, is almost 

 useless without a specific description. The essential discovery 

 made by Bizzozero was not that the blood contained what he 

 described as a third morphological constituent, but that the 

 process of coagulation, as the experiments of Zahn had demon- 

 strated, was due to the formation of white thrombi, which were 

 dependent on the presence of blood-platelets. The coagulation 

 of shed blood in vitro and the local formation of a thrombus 

 are not processes which can fairly be compared together. 

 The knowledge which is obtained from experiments on extra- 

 vascular clotting can certainly not be applied without some 

 reservation to explain the formation of clots when a vessel is 

 transfixed by a needle, or the wall of a vessel is injured by 

 a ligature, or by the application of some damaging reagent such 

 as crystals of sodium chloride or silver nitrate. 



From many experiments it is beyond dispute that masses 

 of platelets can be caused to collect and form a thrombns. 

 A conglutination or aggregation of these bodies occurs at 

 the damaged region. When the rate of flow is artificially 

 reduced, the figures of Eberth and Schimmelbusch l show that 

 although leucocytes can be seen at the edges of the vessel, no 

 platelets are to be observed, these only becoming displayed 

 when the rate of flow is quite slow and just precedes stasis in 

 1 Die Thrombose nach Versuchen und Leichenbefunden, Stuttgard, 1888. 



