t8 THE CIRCULATING LIQUIDS Of THE BOb\ 



5. ' Mast Cells,' or ' Basophiles,' the least numerous variety (o - 5 per 

 cent, of the total number). Very few are to be found in the normal 

 blood of adults, but more in children. They are somewhat smaller 

 than the neutrophiles (average diameter about 10 p.). The nucleus is 

 irregularly trilobed. The protoplasm shows coarse granules, which do 

 not glitter like the granules of the eosinophile cells, and are therefore 

 less conspicuous hi the unstained condition. Unlike the eosinophile 

 granules, they stain with basic dyes, such as methylene blue. 



Blood-Plates, or Thrombocytes. When blood is examined im- 

 mediately after being shed, small colourless bodies (i to 3 // in 

 diameter) of various shapes, but usually round or oval, may be seen. 

 These are the blood-plates or platelets, also called thrombocytes, 

 on account of their function in the coagulation of blood. If the 

 blood is not at once subjected to some procedure which prevents 

 clotting, the platelets swell and then break up. There is reason to 

 believe that in most of the methods of preventing coagulation the 

 essential action is to hinder the break-up of the platelets (p. 37). 

 They can be isolated by receiving a drop of blood from the finger 

 upon a well-cleaned cover-slip, which is then laid, supported by two 

 thin glass fibres, on a carefully cleaned slide. The plasma with the 

 coloured corpuscles and leucocytes are washed away by irrigating 

 the space between slide and slip with a suitable solution, e.g., a 

 salt solution containing a certain proportion of manganese sulphate, 

 which prevents disintegration of the platelets. The platelets stick 

 to the cover-slip (Deetjen). They can then be fixed and stained. 

 The blood-plates can even, like leucocytes, be kept alive on 

 the warm stage in an appropriate medium (agar, to which certain 

 salts have been added), and then show lively amoeboid movements 

 (Deetjen). They have been described as nucleated cells, although 

 the nucleus is not easy to stain, and with the ultra-microscope, a 

 delicate means of testing whether such an object as a platelet is 

 optically homogeneous, no evidence of the presence of a nucleus 

 has been obtained. The origin of the platelets has been a matter of 

 lively controversy. They are not produced by the breaking up of 

 other elements of the shed blood, for they have been observed 

 within the freshly excised, and therefore still living, capillaries 

 in the mesentery of the guinea-pig and rat (Osier). According to 

 the best evidence, they are derivatives neither of the erythro- 

 cytes nor of the leucocytes of the blood, but are developed from 

 special elements (so-called megakaryocytes) of the blood-forming 

 organs (bone-marrow) (J. H. Wright). 



Enumeration of the Blood-Corpuscles. This is done by taking a 

 measured quantity of blood, diluting it to a known extent with a 

 liquid which does not destroy the corpuscles, and counting the 

 number in a given volume of the diluted blood (p. 67) . 



The average number of red corpuscles in a cubic millimetre of 

 blood is about 5,000,000 in a healthy man, and about 4,500,000 in 



