CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 521 



testine, the adenoid tissue, or follicular substance, is the seat of an 

 interaction between the blood and the lymph ; here the blood gives 

 something to and takes something from the lymph, or at least is 

 in some way changed ; here the lymph takes from and gives up to 

 the blood. We may be confident that these changes take place, 

 though our knowledge as to the exact nature of these changes is 

 at present very limited. 



One event taking place in the gland seems tolerably certain. 

 The leucocytes which occupy the meshes of the follicular substance, 

 and the characters of which are similar to those of the leucocytes 

 of a follicle of the intestine, multiply in the follicular substance. 

 Cell-division appears to be particularly active in, but not exclusively 

 confined to, certain areas in the follicles spoken of as lymph-knots 

 or germinal areas. In nuclear-stained sections, that is in prepara- 

 tions so treated that while the nuclei are stained deeply the cell 

 bodies are very lightly stained or not at all, there may be frequently 

 seen in a follicle an area (or more than one area) consisting of a 

 light centre surrounded by a stained ring. In the light centre the 

 cell bodies of the leucocytes are, relatively to the nuclei, larger than 

 in the surrounding zone ; and since the cell bodies are not stained 

 the central portion appears lighter. It is in the clearer central 

 area that nuclei undergoing mitosis, and indicating cell-division, 

 are especially abundant. The surplus cell population thus arising 

 appears to pass, chiefly at all events, into the lymph-sinus, and to 

 leave the gland by the efferent lymphatic vessels ; on examination 

 it is found that lymph which has passed through a number of glands 

 is richer in lymph corpuscles than the lymph which is coming to 

 the glands. 



Many lymphatic glands contain a quantity of black pigment 

 which is chiefly deposited in the branched cells of the reticulum 

 of the lymph-sinuses. This is probably, in many cases at all 

 events, pigment brought to the gland in the lymph vessels, and 

 arrested in its course through the lymph-sinus ; and in the bronchial 

 lymphatic glands the pigment simply consists of minute particles of 

 carbon introduced into the bronchial passages by the inspired air, 

 and carried from the bronchial passages to the glands. In some 

 cases, however, pigment is also found in the bodies of the leuco- 

 cytes of the follicular substance, and this pigment has probably 

 a different origin ; its history and purpose are not however as yet 

 known. 



P. ii. 34 



