THE BLOOD-PLATELETS 



77 



only recognised methods in physiology are those of the chemist 

 and physicist. Views which rely on purely histological evidence 

 often have but a short-lived existence, and though it would be 

 both invidious and profitless work to point out how frequently 

 the inferences derived from histological observations have been 

 shown to be misleading, the history of physiology and pathology 

 abounds with such examples. 



Descriptions of the platelets as they occur in mammalian 

 blood are not in complete agreement. As to their size, aspect, 

 peculiar green tint, and amount of granulation in a hyaline plasm, 

 most observers are in accord. Among disputed points we may 

 mention the presence or absence of haemoglobin, the possession 

 of a nucleus, their alteration in shape and power of locomotion ; 

 and with reference to all these differences, some of which are 

 of cardinal importance, there is absolutely no agreement. For 

 example, Hayem affirms that the platelets contain haemoglobin, 

 a statement unconfirmed by Bizzozero. The nucleus described 

 by Deetjen and Dekhuyzen, and shown in the illustration 

 given by Kopsch, 1 is undescribed by Bizzozero, and, according 

 to Kemp, is only a central collection of granules. Schneider 2 

 denies that the platelets are locomotive, a statement with which 

 we entirely agree. The number of platelets in human blood is 

 exceedingly variable ; the average number per cubic millimetre 

 is given in the following table : 



In mammalian blood the platelets vary in size and aspect 



1 "Die Thrombocyten des Menschenblutes," Anat. Anzeiger, xix. 1901. 

 "Beitrage dur Frage der Blutplattchengenese," Virch. Archiv, clxxiv. 1903. 



