98 A TEXTBOOK OF PHYSIOLOGY 



The 'eosinophil corpuscles are also polyraorphonuclear, but their 

 big red granules are easily seen under the >. objective. 



The rare basophil cell (sometimes called a mast cell) has large 

 blue granules. 



In numbers the pale corpuscles vary from 5,000 to 8,000 per cubic 

 millimetre. If they are much above this number, the condition of 

 leucocytosis is said to exist; below that, of leucopenia. 



A differential blood-count of the pale corpuscles (i.e., the relative 

 percentage of each corpuscle) of a film shows that there is in normal 

 blood usually 75 per cent, leucocytes and 25 per cent, lymphocytes. 

 The leucocytes are divided as follows: Neutrophils 71 to 73 per 

 cent., eosinophils 2 to 4 per cent., basophils 0-5 per cent, or 

 less. Morbid conditions which cause large numbers of basophils to 

 appear in the blood are extremely serious, and for this reason they 

 have been termed " the harbingers of death." Of the 25 per cent, 

 of tymphocytes, normally 23 per cent, are small, 2 per cent, 

 large ; these numbers vary slightly, but any large variation is regarded 

 as pathological. 



In the horse the number of leucocytes per cubic millimetre of blood 

 is 8,000 to 11,000; in the ox, 7,000 to 9,000; goat, 9,000 to 12,000; 

 sheep, 9,000; pig, 16,000. 



The proportion of leucocytes to lymphocytes also differs, lympho- 

 cytes forming 30 per cent, of the total in the pig, 30 to 40 per cent, 

 in the horse, 25 to 35 per cent, in the ox. 



The Origin of the Pale Corpuscles. Although, as stated above, it 

 is generally held that the leucocytes and lymphocytes have a separate 

 origin, especially in adult life, the leucocytes arising from myelocytes 

 in the bone marrow, and the lymphocytes from lymphatic tissue, 

 there are some authorities who believe that in foetal life the hsemo- 

 blast affords an origin for all the other forms of corpuscles (see 

 table, p. 89). 



The Functions of the Pale Corpuscles. The leucocytes by virtue 

 of their amoeboid or pseudopodial movements can surround particles 

 of foreign material and take them into their substance. For 

 this reason they are termed phagocytes. By virtue of their phago- 

 cytic action the leucocytes play a great part in defending the body 

 from the onslaught of invading microbes, emigrating from the vessel? 

 for the purpose (Fig. 24). They also probably play a part in forming 

 the protective substances of the plasma, such as antigen, complement, 

 and opsonin (see p. 109). When blood is shed, these corpuscles help 

 to produce the clotting of blood. 



The lymphocytes play a part in the absorption of fat, and 

 possibly in uric acid metabolism. 



Enumeration of White Corpuscles. The pale corpuscles may be 

 counted by the Thoma-Zeiss instrument. In this case the pipette 

 giving the smaller dilution 1 in 10 (labelled 11) is used. The usual 

 diluting fluid contains 0-3 per cent, acetic acid tinted with methyl 

 green. The weak acid destroys the red corpuscles, and the methyl 



