1 8 A MANUAL OF PHYSIOLOGY 



5. ' Mast Cells,' or ' Basophiles,' the least numerous variety (0-5 

 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 /*). 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 in the unstained condition. 

 Unlike the eosinophile granules, they stain with basic dyes, such as 

 methylene blue. 



Blood-plates. When blood is examined immediately after 

 being shed, small colourless bodies (i to 3 /j, in diameter) of 

 various shapes, but usually round or oval, may be seen. These 

 are the blood-plates or platelets. They can be collected by 

 placing a drop of blood on a smooth and clean piece of paraffin, 

 and keeping it in a moist chamber. Clotting is long delayed, 

 and the white and coloured corpuscles sink to the bottom, while 

 the platelets rise to the top of the drop, from which they can be 

 removed by a cover-slip. They can be best studied when the 

 blood is mixed directly with some fixing solution, such as 

 Hayem's solution (sodium chloride, I grm. ; sodium sulphate, 

 5 grm. ; mercuric chloride, 0-5 grm. ; water, 200 grm.), or osmic 

 acid. They 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 move- 

 ments (Deetjen). While some observers believe that they 

 represent the remains of the nuclei of the erythroblasts, it is 

 more probable that they are independent elements. They 

 have even been described as nucleated cells, although the 

 nucleus is not easy to stain. 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). 



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. 58). 



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 a healthy woman, but a variation of 1,000,000 up or down 

 can hardly be considered abnormal. In persons suffering from 

 profound anaemia the number may sink to 1,000,000 per cubic 

 millimetre, or even less, while in new-born children and in the 

 inhabitants of high plateaus or mountains it may rise to 7,000,000, 

 or even more. In the latter instance a residence of a fortnight 

 in the rarefied air is sufficient to bring about the increase, 



