52 THE BODY AT WORK 



connective tissue beneath the mucous membrane of the whole 

 of the respiratory tract trachea, bronchi, and bronchioles 

 is diffuse adenoid tissue. It presents no special structure, but 

 its spaces are packed with leucocytes in various stages of cell 

 division, and young leucocytes, or lymphocytes, as they are 

 usually named. Some of the lymphocytes make their way into 

 the blood or into the lymph. Others, acquiring their full 

 dimensions, scour the epithelium which lines the respiratory 

 tract for germs and other foreign bodies which are drawn into 

 the tract with inspired air. They may be seen pushing aside 

 the cells of the lower strata of the epithelium, on their way to 

 the surface, or returning to the subepithelial connective tissue 

 with germs, or particles of soot, or debris of epithelial cells 

 which they have taken into their substance (Fig. 4, B). 



The tonsils are examples of follicular lymphoid structures. 

 They lie one on either side of the entrance to the gullet, 

 between the two folds (the anterior and posterior pillars of 

 the fauces) by which the soft palate is continued to the side 

 of the tongue. Normally the tonsil is not visible, but when 

 inflamed it may project sufficiently to be seen ; and its surface 

 may then be covered with mucus and pus. It is liable to 

 become enlarged in childhood, owing to chronic inflammation. 

 A section of the tonsil shows it to consist of clusters of lymph- 

 follicles lying beneath the mucous membrane. The term 

 " follicle " is unfortunate. It conveys no idea of the form 

 or structure of one of these masses of lymph-cells ; and it is, 

 besides, applied to things of an entirely different character 

 for example, the pits of mucous membrane which sink down 

 between the masses of lymphoid tissue in the tonsil. The 

 expression " follicular tonsillitis " does not refer to the lymph- 

 follicles, but to the epithelial pits. It is a condition in which 

 a drop of pus is to be seen in the mouth of each of the pits. 

 A lymph-follicle is a small rounded clump of connective tissue, 

 denser on its periphery than in its centre. Its bloodvessels 

 are disposed chiefly on the periphery. Lymphatic streamlets 

 arise in the centre. Its outer portion is closely packed with 

 dividing lymph-cells and young leucocytes, which as fast as 

 they are formed migrate towards the centre, and eventually 

 escape from the follicle by the lymphatic vessels. The con- 

 nective tissue which invests and separates the follicles is full 



