ORGANS OF THE BODY. 



453 



smoke, and loaded with soot, it is found in large quantities, it was 

 inferred that the true origin of the pigmentation must lie in the inspira- 

 tion of particles of carbonaceous matter. This view seems to be confirmed, 

 farther, by observations made on the organs of those engaged in occupa- 

 tions which necessitate their breathing an air charged with supended dust 

 of various kinds, as, for instance, those of coal miners, whose lungs may 

 be found to be perfectly black. It was also discovered that large frag- 

 ments of wood charcoal often make their way into the air vesicles, and 

 that the lungs of animals, when confined in sooty chambers, become quite 

 black (Knauff}. That a deposit of genuine melanin, however, does 

 also take place in the lungs and air passages, as well as in the bronchial 

 glands, is beyond doubt, but we are unfortunately unable as yet to dis- 

 tinguish between the two kinds of particles. 



REMARKS. A distinction between " anthrakosis " and "mclanosis" of the respira- 

 tory organs may be made. The cells which we have given in fig. 95, frequent con- 

 stituents of the sputa, are in many instances genuine melanin cells ; "but in other 

 cases which may be set down as more the rule, the contractile body of the cell has 

 taken up fine carbonaceous particles from without. We nmst confess, however, that 

 the deposit of these matters in the interstitial connective-tissue of the lung and 

 parenchyma of the bronchial glands is still a subject of great obscurity. 



242. 



There now remain for our consideration but a few more structural 

 relations in dealing with the lung. There are the arrangement of its 

 blood and lymphatic vessels, epithelium of the air vesicles, nerves, and 

 serous covering. 



The blood-vessels of the organ receive their blood, as is well known, 

 from two sources: firstly, from the bronchial; secondly, from the pul- 

 monary arteries. The first of these serve the subordinate purpose of yield- 

 ing nourishment to the tissue of the organ ; the second are set apart for the 

 requirements of respiration. The distinc- 

 tion between the two, however, is by no 

 means sharp. 



The arteria pulmonalis divides and sub- 

 divides, following the ramifications of the 

 bronchi, and arrives thus with its twigs 

 between the lobuli. Here a further split- 

 ting up occurs until very fine tubes are 

 formed, which penetrate into the elastic 

 band-work between the pulmonary vesicles 

 (fig. 434), often sub-dividing still further in 

 their course here. At the same time, the 

 most extensive anastomosis takes place, so 

 that imperfect or even complete rings are 

 formed (b). From these a multitude of 

 capillary tubes is given off to form the 

 respiratory capillary network, which clothes 

 the walls of the air-vesicles, only separated 

 from the atmospheric air by the most deli- 

 cate membrane. 



This network (a) is remarkable for the great regularity and small size 

 of its meshes. It may be reckoned among the densest, as also the most 

 regular occurring in the body. The peculiar form of its wide capillaries 

 is also striking. The diameter of the latter is about 0-0056-0-0113 mm.. 



Fig. 434. The respiratory capillary net- 

 work of a horse's lung, injected 

 after GerlacKs method. 6, the end 

 branches of the arteria pulmonalis 

 encircling more or less the several 

 pulmonary vesicles; a, the capillary 

 system. 



