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 débris 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 connective tissue which invests and separates the follicles is full of leucocytes. Removal of the tonsils is followed by no ill effects. They are not essential to our well-being. Nevertheless, they have important functions to perform. They are barracks crowded with leucocytes, which guard the pass into the alimentary canal. Their leucocytes incessantly patrol the mucous membrane, capturing germs, removing fragments of injured epithelium, striving to make good the mischief to which this part of the alimentary canal is peculiarly liable. The enlargement of the tonsil which results from frequent sore throat is a response to the demand for an increase in the supply of these little scavengers, in order that they may cope, not only