The blood platelets, the third corpuscular element of the blood, have since the fundamental work of Bizzozero, been the object of many researches, the results of which, in brief, are the following:
The platelets are a normal element of the blood of great importance for coagulation and thrombosis.
The place of origin of these bodies is not known with absolute certainty, although most authors believe in Wright's theory, that traces their descent to the megakaryocytes of the bone marrow.
The platelet count normally varies more than does the number of red and white cells.
The platelet count is low in genuine, idiopathic purpura, and in certain diseases of the blood and infections (pernicious anemia and typhoid).
When the number of platelets falls below certain values, the symptoms of a hemorrhagic diathesis occur.
The methods for counting the platelets hitherto published, all use blood from a skin prick and may be divided in two groups