A TEXTBOOK OF PHYSIOLOGY 



looked upon as a third kind of blood-corpuscle; according to the 

 others they are but artefacts. A great diversity of opinion exists 

 among the supporters of the view that they are a true corpuscle. 

 They are variously stated to be amoeboid and non-amoeboid; nucleated 

 and non-nucleated. Their diameter is 2-3 ^ They are best seen if a 

 drop of blood is received on to a block of paraffin wax and placed in a 

 moist chamber. The blood does not coagulate when thus received 

 on wax. At the end of twenty minutes most of the red corpuscles 

 have sunk to the bottom of the drop. The platelets, being lightest, 

 remain at the top of the drop, and, if this be gently removed, large 

 numbers of platelets will be seen. 



Platelets increase in number after the blood is shed. In a well- 

 made blood-film few or no platelets are seen. If, however, the blood 

 is allowed to stay on the slide some time before being drawn into a 

 film, it will be found that many bodies which might be termed blood- 

 platelets are visible. 



It seems probable that they are to be looked upon as artefacts, 

 and may be grouped into four categories: 



1. Platelets containing haemoglobin. 



2. Platelets containing no haemoglobin. 



3. Platelets with an inner body. 



4. Platelets without an inner body. 



In normal blood there exist few, if any, platelets, and such as 

 exist are generally clumped together. They separate from the 

 plasma owing to contact with foreign bodies, and in part owing to 

 the lowering of temperature. The addition of so-called fixing and 

 indifferent fluids may produce enormous numbers of them, the number 

 varying for different fluids. On adding a metaphosphate solution to 

 blocd the platelets appear suddenly, and belong to the amoeboid type ; 

 when a solution of potassium oxalate is used, they are at first of this 

 type, but afterwards appear as pin-like and tailed bodies; subse- 

 quently small bodies are extruded from the red corpuscles. These 

 bodies stain differently, and resemble bodies which form in coagulating 

 blood after the administration of certain poisons. It is possible that 

 a few platelets of this type may exist in normal blood. The exact 

 source of origin is not known; they may arise from the fragmentation 

 of red corpuscles, possibly the fragmentation of pale corpuscles, but 

 generally are regarded as fine deposits of the blood-proteins. When 

 first discovered they were regarded as young red corpuscles, after- 

 wards they were thought to be young white corpuscles; both views 

 are now known to be wrong. 



Recently a compromise between the divergent views has been 

 suggested, and the platelets grouped into " platelets " true corpuscles, 

 which are believed to play some part in the coagulation of the 

 blood, and "blood-dust" protein granules of about 1^, known as 

 haemoconea. " Blood-dust " is insoluble in alcohol or ether, and is not 

 blackened by osmic acid. Some regard it as formed of the extruded 

 granules of the pale corpuscles. 



