54 THE BODY AT WORK 



molecules are oxidized and replaced by new material. It is 

 not L improbable, therefore, that there is a difference between 

 the ^metabolism of the fixed tissues and the metabolism of 

 leucocytes. Tfie whole of a wandering cell, its nucleus 

 included, breaks down and has to be removed. We do not 

 know that this occurs in the case of a fixed cell. On the 

 strength of evidence which points, apparently, to a chemical 

 relationship between nuclear substances and uric acid, it has 

 been inferred that the two chief nitrogenous products which 

 are excreted by the kidney are divisible into the one which 

 in the main represents the oxidation of fixed cells, urea, and 

 the other, uric acid, largely derived from the oxidation of 

 wandering cells. 



The valiant leucocytes do their best to cope with all the 

 rubbish, whether living or dead, that needs removal. They 

 flock to any situation in which germs are numerous or tissue 

 has been destroyed. If all goes well they take the foreign 

 matter into their substance dead tissue is matter foreign to 

 the body and either digest it in the course of their ordinary 

 progress, or retreat with it, if they cannot digest it, to the 

 nearest lymphatic gland. But in their efforts to reach objec- 

 tionable matter they are apt to wander too far from the 

 healthy lymph from which they obtain oxygen for their own 

 respiration. Unable to breathe, they die. They lose the 

 power of extruding pseudopodia. Their extensible, prehensile 

 processes are drawn in. Assuming a globular form, they float 

 helplessly in what once was lymph. Their body-proteins are 

 largely changed to fat. As " pus cells," they are thrown off 

 in the discharge from an ulcer, or accumulate in the cavity 

 of an abscess. A pus cell is a dead and fattily degenerated 

 leucocyte. 



The third kind of breeding-place of leucocytes, a lymphatic 

 gland, has a more elaborate structure than the tissues with 

 which we have already dealt. Lymphatic glands are about 

 the size of beans, and of the same shape. They are found in 

 the course of lymphatic vessels in situations where they are 

 not exposed to pressure, such as the back of the knee, the 

 groin, the front of the elbow, the armpit, in the neck above 

 the collar-bone, and on either side of the sterno-mastoid muscle, 

 behind the angle of the jaw. There are a number in the 



