"Blood cell #cosplay” is a thing! Here's a typical "platelet" costume based on the “Cells at Work!” (はたらく細胞) manga series. Platelets are usually depicted as children, since they’re small. Giant platelet image: @ASH_hematology. #HematologyTweetstory 16 is about platelets./1 
Long ago, for a medical-themed costume party, I dressed as a "platelet clump", plastering myself with small paper plates complete with ultrastructure drawings. Was so nerdy, I’m embarrassed to admit it; I hope no photos survive. My getup was nowhere near as nice as this dress./2
RBCs were first seen under a microscope by Jan Swammerdam (1637–1680) & his acquaintance Antoni van Leeuwenhoek (1632–1723) in the Netherlands, and by Marcello Malpighi (1628-1694) in Rome. For >150 years, anyone looking at blood under the microscope apparently only noticed RBCs.
White cells weren't described until the 1840s: by Gabriel Andral (1797–1876) in France & William Addison (1802–1881) in England. Paul Ehrlich first stained WBCs ~1879-1880 & distinguished subtypes: neutrophils, basophils and eosinophils, based on their affinity for dyes./4
In order to see #platelets, microscopes had to get an order of magnitude better than they were in the 1600s. Achromatic (ie free of chromatic aberration, illustrated on the R below) and aplanatic (free of spherical aberration, L) microscopes were first produced only circa 1830./5
Alfred François Donné (1801-1878) in Paris, a pioneer in microscopy and photography in the era of daguerrotypes, may have been the first to detect the third major blood cell type: platelets. In 1842 he noted tiny particles in the blood; he thought they were fat/chyle globules./6
In the 1840s, George Gulliver (1804-1882) in England described vague particles that may also have been platelets. In 1864 Lionel Smith Beale (1828-1906) drew platelets. Addison, mentioned above, drew a fibrin clot in 1842 that looks like it includes platelets (depicted below).
In 1865, cell theory pioneer & @UniBonn Anatomy chair Max Schultze (1825-1874) noticed small cell-like elements in blood clots. He suggested they were worthy of further study. He called them “Körnchenbildungen” – granule formations. Others called them "Max Schultze’s corpuscles".
I am glad "Max Schultze corpuscle" didn’t last. Can you imagine someone saying, “We’re need to consult hematology about those low Max Schultze’s corpuscles”, or a med student on rounds (eg here @PennMedicine): “The patient presented last night with severe maxschultze-penia"😜
Anyway, there was a lot of debate about just what these curious little blood granules were. In France, Georges Hayem and Georges Pouchet thought they were RBC precursors. Ernst Neumann and several German investigators thought they were RBC *breakdown* products instead./10
Osler, a student of platelets, thought Hayem’s idea that platelets became RBCs was just silly. He joked, “I have spent many weary hours over them, but I never caught one 'blushing.'” Ah, but Osler had never seen blood cell manga cosplay! Here in fact is a "blushing platelet".
While Osler clearly observed platelets in 1874 and made some nice sketches (below, left), he wasn’t sure if they were a normal human cell or some sort of exogenous microorganism. He called them “blood plaques.” Others called them “blood dust”, which is a pretty cool metaphor./12
In 1882, Giulio Bizzozero in Turin (1846-1901; he's “Julius” in German literature) published a monster paper, 71 pages & 25,000 words, about the new cells & their role in clotting: “Über einen neuen Forrnbestandteil des Blutes und dessen Rolle bei der Thrombose und Blutgerinnung”
Bizzozero called these granules "piastrine" – i.e., “small plates” - in his Italian-language papers, "petite plaques" or "plaquettes" when he was writing in French, and the diminutive "Blutplättchen" in German. Maybe he got the idea from a restaurant menu? 😉 /14
A key insight into platelet function came from @MassGeneralNews in 1909. A 20 year-old Armenian tailor presented to #MGH w/ epistaxis and was found to have a platelet count of 6,000/mm3. He was given a “large amount of blood"; platelets went up to 123,000/mm3 & bleeding stopped!
A pathology resident at #MGH, W.W. Duke (1882-1945; after 1912 in clinical practice in Kansas City), invented a way of measuring bleeding. He cut the tailor's earlobe and measured how long the bleeding took to stop pre- and post-transfusion. This was the first “bleeding time”.
James Homer Wright (1869–1928) was Chief of @MGHPathology from 1896-1926. Together with Richard Cabot, in 1915 he began the series of "Case Records of the Massachusetts General Hospital", which continues in @NEJM to this day. Wright gave platelets the name we use today./17
In a 1906 paper, Wright 1st described how “blood plates” come from "giant cells" in the marrow. Perhaps recognizing Bizzozero’s contributions, in 1910 Wright began calling the tiny cells that contributed to clots and whose absence caused bleeding “platelets”. The name stuck./18
The history of platelet discoveries after 1910 is too complicated to go into here, but there are many reviews. @BostonChildrens Alan Michelson’s platelet textbook is good, and Douglas Brewer, emeritus anatomy professor in #Birmingham, wrote a nice 2006 review @BritSocHaem /End
