1874.] the Lymphatic System of the Lungs. 139 



phangial new growth takes place on the peribronchial lymphatics. From 

 the study of the normal lung, it can be ascertained that not all the large 

 branches of blood-vessels are accompanied by lymphatics, and not even 

 one and the same branch for its whole length, but that in some places 

 they are only surrounded by branched connective-tissue corpuscles, which 

 may be said to belong to their adventitia. In a given case, one will not 

 be able to determine whether a certain tubercular cord has developed by 

 the increase of these adventitial cells, or whether it has developed from 

 the endothelium of a lymphatic, either as a peri- or endolymphangial cord ; 

 for the fully developed cords have quite the same relation to the blood- 

 vessels as if they had developed in their adventitia. 



I have already mentioned that the growth of adenoid tissue in the 

 branches of the subpleural lymphatics extends to the connective-tissue 

 corpuscles between the alveoli. Exactly in the same way we see the pe- 

 rivascular adenoid cords spreading between the alveoli ; that is to say, the 

 perilymphangial growth of tracts of adenoid tissue extends from the lym- 

 phatics to the interalveolar branched cells, with which the endothelium 

 of the former is in direct continuity. 



The first points at which the tubercular perivascular cords of adenoid 

 tissue make their appearance are the ultimate branches of the pulmonary 

 artery and vein, whence they spread along the lymphatics towards the 

 larger branches, as well as towards the interalveolar branched cells. In 

 general the growth in the first direction (that is, towards the larger 

 branches) goes on much more abundantly and rapidly than in the other 

 direction. 



It is an important fact that I have constantlymet with the following con- 

 dition of the tuberculous lungs of guineapigs : The ultimate branches of 

 the pulmonary artery show a germination of their endothelium, which is 

 already recognizable in the earlier stages of the disease, at a time when 

 perivascular cords are only rarely to be found. If the process advances, the 

 germination of that endobheliurn reaches such a degree that the cavities of 

 the blood-vessels are almost filled with its products, only a very narrow 

 central canal being left free. In later stages, the tunica media of the 

 smaller and middle-sized vessels, that are provided with perivascular cords , 

 becomes very much thickened, and splits into laminae, between which lie 

 accumulated lymphoid cells, either free or contained in a reticulum. In 

 many places it can be shown that the adenoid tissue of the perivascular cords 

 gradually grows towards the cavities of the vessels, and finally assumes the 

 whole portion of the vessel into its substance. The chief fact of import- 

 ance, however, is that the capillary blood-vessels of those interalveolar 

 trabeculaB, into which the perivascular cords have penetrated, have become 

 converted into solid nucleated bands and threads, which are in continuity 

 with the surrounding reticulum. These threads, although they appear 

 solid, must be taken as still permeable by fluid substances ; for in lungs 

 the pulmonary artery of which had been previously injected with a cold 



