in.] BLOOD-PLATELETS. 123 



19. Blood-Plates or Platelets (H). Wrap a handkerchief round a finger to 

 obtain some blood (Lesson III., p. 115). On the skin at the root of the nail 

 place a drop of normal saline containing methyl-violet (.75 gram in icoocc.). 

 Through this drop prick the finger, and blood runs into it. Place a little of the 

 mixed blood and methyl-violet solution on a slide ; cover at once and examine. 



It requires a good microscope arid careful observation to see the platelets. 

 The red corpuscles are unstained while the colourless corpuscles are stained. In 

 the field are to be seen small oval, refractive, very delicate, non-nucleated 

 bodies, much smaller than the red corpuscles 

 these are the blood-plates (fig. 83, 3). They 



are about 2. 5 /tin diameter. They undergo f#jj\ ^ o 



cceedingly rapidly in shed blood. % IflpJ ^^ 



changes exceedingly rapidly in shed blood. 



Instead of methyl-violet solution, the skin 

 may be pricked through a drop of the follow- 

 ing mixture: I part of I per cent, osmic 

 acid, and 2 parts .75 per cent, sodic chloride. 



By far the best method of obtaining blood- 

 platelets in large quantity, and in a condition 

 in which they do not disappear, is to allow 

 blood to flow into a solution of oxalate of 



. i i-l.l i i .1 WltllO. I 1 M M l-l Mill I',-) , l . I;>II11MI 



potash until the mixture contains at least corpuscle surrounded by blood- 



I per 1000 of the salt. This prevents coagula- plates. 



tion of the blood. On placing such blood in a 



centrifuge, when the corpuscles subside a film of grayish material accumulates 



on their surface, which consists chiefly of blood-plates. A drop of this spread 



on a slide, dried, and stained with a watery solution of methyl-violet 5 B and 



mounted in balsam, yields permanent preparations of these bodies (Moser}. 



20. Blood-PlateletsDry Method (H). Clean a slide thoroughly ; sterilise 

 it in the flame of a Bunsen-burner, and allow it to cool. Obtain a drop of 

 blood from the finger in the usual way ; get a drop on the slide, and with the 

 edge of another slide rapidly spread the drop of blood as a thin film on the 

 sterilised slide. Move the slide to and fro in the air until the film of blood 

 dries. The whole process should not occupy more than four seconds. Cover 

 the dry film with a cover-glass and seal the latter at the corners with paraffin. 



(a.) Observe the coloured blood-corpuscles, which for the most part retain 

 their shape, and between them the blood-platelets or, as Hayem calls them, 

 the hnematoblasts. They are readily seen thus in human blood. The white 

 corpuscles are somewhat altered in shape. 



21. Weigert's Method of Staining Fibrin. Embed a thrombus or a piece 

 of lung affected with acute croupous pneumonia in celloidin, and make a 

 section. Float the section from water on to a slide. Stain it for ten minutes 

 or so with a drop of the following fluid : 



Gentian violet (5 per cent.) . . 4400. 

 Aniline oil ..... i ,, 

 Alcohol (96 per cent. ) . . 6 , , 



Remove the stain by pressing on the section two or three plies of blotting- 

 paper, or, better, unsi/ed printing-paper. Add a drop of iodine in iodide of 

 potassium (iodide of potassium 5 per cent, and saturated Avith iodine). This 

 quickly decolorises most of the stained parts. Remove the iodine with blot- 

 ting-paper in the same way as before. 



Pour on the section a mixture of equal volumes of xylol and aniline oil, 

 moving the mixture over the preparation. Remove ihis and apply a fresh 

 supply of the xylol-aniline oil mixture. This removes all the water. As 

 long sis there is a trace of whiteness in the section it still contains water. 

 After all the water is removed, dry the preparation with paper as before, to 



