116 PHYSIOLOGY CHAP. 



digestion of the microbes englobed by leucocytes (anthrax bacilli, 

 spirilli of recurrent fever, vibrios of septicaemia, streptococci of 

 erysipelas) have been directly observed in various phases. These 

 facts are much in favour of Metchnikoff s view that the protoplasm 

 of leucocytes contains enzymes .which are more active than the 

 secretions of the digestive glands of higher animals (pepsin and 

 trypsin), since the latter fail to kill the same microbes. 



According to Leber, Massart, Bordet and other observers, the 

 migratory and phagocytic faculties of the white corpuscles are 

 phenomena of chemotaxis (i.e. the property of being attracted or 

 repelled by certain chemical compounds, even at a distance). It 

 is a fact that leucocytes do not devour all the species of microbes 

 which they encounter in their wanderings, but are capable (at least 

 up to a certain point) of selecting the prey on which they feed. 

 In the body the physiological function of the leucocytes depends 

 essentially, as we shall see below, upon their phagocytic capacity. 



The number of leucocytes varies conspicuously, even under 

 physiological conditions. This may partially at least be ex- 

 plained by the fact that they are continually (in different degrees, 

 according to the functional state of the viscera) emigrating from 

 the lymphatic system, in which they originate, to the vascular 

 system, and thence again by diapedesis into the lymphatic system. 



The method for counting leucocytes is fundamentally the 

 same as for the enumeration of erythrocytes. In normal blood 

 their number is much lower than that of the erythrocytes. 

 According to Grancher, there are in healthy young people of 

 twenty to thirty, 3000 to 9000 leucocytes in 1 c.mm. at different 

 hours of the day. The ordinary ratio between these and the 

 erythrocytes would be from 1:1200 to 1:1500, but it may increase 

 to a maximum of 1:900. According to Malassez, on the other 

 hand, there are 4000-7000 leucocytes per c.mm. in healthy persons ; 

 and the ratio with the erythrocytes is from 1:1250 to 1:1650. 

 It must always be remembered that the number of leucocytes 

 varies according to the vascular region from which the blood is 

 drawn, and with age, season, state of nutrition, in menstruation, 

 pregnancy, etc. Disease has the greatest influence on the number 

 of leucocytes ; during suppuration, but especially in certain 

 morbid states (leucaemia), their numbers may be enormously 

 increased, and their ratio with the red corpuscles may rise to 1:15 

 or even higher. On the other hand, it should be noted that the 

 opposite occurs during the first week of an absolute fast, when 

 there is marked and progressive diminution of the leucocytes 

 (Luciani). 



It has not hitherto been found possible to examine the 

 chemical composition of the leucocytes of the blood, owing to the 

 difficulty of separating them from the plasma without admixture 

 of other elements. The first observations on this subject were 



