156 ESSENTIALS OF PHYSIOLOGY. 



shape of the red corpuscle is the same as that of the human erythrocyte ; 

 in camels the corpuscle is oval and biconcave. 



The white blood corpuscle is a colourless, nucleated cell, and several 

 varieties occur in human blood. The most abundant type, forming 

 about 70 per cent, of the total number of leucocytes, is the polymorpho- 

 nuclear, so called because the nucleus consists of lobes, connected by 

 finer strands. This cell is rather larger than the erythrocyte, being 

 about 10/x, in diameter. It possesses the power of amoeboid movement, 

 and, because of its function of ingesting bacteria and foreign particles, is 

 said to be phagocytic. Its protoplasm contains numerous fine granules 

 which stain with neutral dyes, and are described as neutrophile. A 

 somewhat similar corpuscle, in which, however, the nucleus is usually 

 horse-shoe-shaped, contains large granules which stain deeply with acid 

 dyes, such as eosin. These cells are called eosinophile. They form from 

 1 to 5 per cent, of the total number of leucocytes. A basophile variety, 

 in which the granules stain with such basic dyes as methylene blue, is 

 found only occasionally in normal blood. Small and large lymphocytes 

 form about 25 per cent, of the total number of leucocytes, the small 

 variety being the more numerous. Lymphocytes are distinguished by 

 containing a large spherical nucleus surrounded by a small amount of 

 hyaline protoplasm, which does not contain granules. 



Other bodies, called blood-platelets, are found in recently shed blood, 

 but these cannot be seen when precautions are taken to prevent 

 the blood coming in contact with foreign substances ; and it is believed 

 that they are not a formed constituent of normal blood. Blood-platelets 

 are colourless bodies, one-third to one-half the size of red corpuscles, 

 and each contains a central group of granules resembling a nucleus. If 

 examined on metaphosphate agar, the platelets show amoeboid movement. 



The blood of a healthy man contains about 5,000,000 red corpuscles 

 in each cubic millimetre, that of a woman about 4,500,000. The 

 corpuscles are counted by means of a heemocytometer. This consists 

 of a glass cell of known depth, the floor of which is ruled in squares of 

 known size. The blood is diluted 100 times with a slightly hypotonic 

 solution of sodium sulphate, which prevents coagulation, and the cell is 

 filled with the mixture. The corpuscles settle on the squares and can 

 be counted under the microscope. The volume corresponding with each 

 square and the dilution of the blood being known, the number of 

 corpuscles per cubic mm. of blood can be calculated. The number is 

 diminished by haemorrhage and in certain diseases, and is increased by 

 living at high altitudes. 



The white corpuscles number about 10,000 in each cubic millimetre 

 of blood. They can be counted by means of the hsemocytometer, the 



