ORGANS OF THE BODY. 419 



body, manifested by inflammatory appearances and swellings of these 

 organs. 



Thus we see that the lymphatic glands of man are liable to vary much 

 in structural appearance, which must be partly attributable, no doubt, to 

 the metamorphoses accompanying increasing age. 



Among the latter may be reckoned the partial transformation of the 

 connective-tissue framework into fat cells, and degeneration of the reticular 

 connective substance into ordinary fibrous tissue, with consequent gradual 

 obliteration of the whole organ. 



A third change observable in lymph nodes is true pigmentation. This 

 affects principally the bronchial glands, and is almost invariably to be 

 met with after a certain age, though with varying degrees of intensity. 

 It may be due to the irritation of inflammation in the pectoral organs. 

 Small granules of melanin (p. 52) are formed by the gradual metamor- 

 phosis of the colouring matter of the blood. But though this may be 

 accepted as one source of black pigmentary molecules, the latter have a 

 very different origin, most probably, in many other cases. They are, 

 namely, particles of carbon in a state of the most minute division, given 

 off as soot from lamps, &c., and inspired and conveyed from the lungs 

 into the lymphatic glands (Knavff). But between these two kinds of 

 molecules we are at present unable to distinguish with any certainty. 

 They lie utterly without order, partly within the lymph corpuscles, and 

 in peculiar lumpy masses, and partly in the ground-work of the septa and 

 walls of the vessels. In some instances the follicles appear to be the 

 parts most affected, in others the lymph tubes of the medulla. A slight 

 amount of this "melanosis" communicates to the bronchial glands a 

 mottled appearance, while strongly marked it may cause the whole organ 

 to appear uniformly black. 



The effect on the lymphatic glands of inflammation of neighbouring 

 parts is most evident. The meshes become narrower in the framework ; 

 the bodies of the cells of the same become plump, their nuclei undergo 

 division, while great distension of the capillaries is also observed, in 

 fact, the whole gland acquires more or less the appearance it presented at 

 an earlier age. Later on the reticular framework may grow luxuriantly, 

 the distinction between medulla and cortex ceases to be apparent, the 

 lymphatic system of canals disappears, and the whole organ becomes in- 

 capable of functionating. 



The derelopment of the lymphatic glands in the embryo, as well as 

 their nature, was until quite recently entirely unknown. That their 

 origin, together with the whole vascular system, was from the middle 

 germinal plate, is all that was known about them. This had been demon- 

 strated years ago by Remak. The labours of Sertoli and Orth, however, 

 have recently thrown some light upon the subject as regards these points. 

 According to the interesting, but by no means exhaustive treatise of the 

 first of these observers, there may be seen in the mesenteric glands of the 

 ox, in the first place, a system of lymphatic canals at that spot where 

 the connective-tissue nucleus or hilus-stroma of His is to be found. 

 Around this system a quantity of connective-tissue, rich in lymph cor- 

 puscles, is gradually developed, from which the cortical substance, in the 

 first place, takes its rise, and then the lymph tubes of the medulla. The 

 investing spaces and cavernous passages of the medulla make their 

 appearance subsequently, as well as the capsule, septa, and reticulated 

 tissue connected with the latter. 



