14,5 



of the capillaries being very thin, enables the process to spread easily all 

 round. The perivascular connective tissue is hyperaemic and is 

 depositing fibrine. The wall of the lymph vessel is infiltrated, and dense 

 crowds of lencocytes surround the lumina of the larger vessels. These 

 phenomena, which are found to have changed still further in older stages, 

 are true perilymphangitic processes. At the same time no changes have 

 taken place in the blood vessels or their capillaries. Only after the 

 exudation has reached huge dimensions and the supporting tissue has 

 been pushed apart, and after subsequent invasion of fibroplasts, we find 

 stasis in the blood vessels. Pari passu with the advance of the disease, 

 the capillaries of the inters titities become more and more dilated and 

 distended with erythrocytes. 



The denser the neoplastic connective tissue of the perilymphangitis, 

 the more readily are the walls of the blood capillaries damaged by the 

 toxine of pleuro-pneumonia virus. Exudation of fibrine and formation of 

 thrombus are the consequence. Disturbances in the circulation and con- 

 sequitive lesions of the walls of the vessels are responsible for the develop- 

 ment of these phenomena. In the smaller vessels one usually finds 

 small mixed thrombus with layers of fibrine on the walls ; in the larger, 

 trabecular masses fill the lumen. 



The streaks of blood-platelets are fianked by walls or rings of leucocytes, 

 from which fibrine mixed with erythrocytes form loops connecting the 

 various streaks. In older stages one finds thick neoplastic connective 

 tissue around the pulmonary veins, perforated .and penetrated by loose 

 fibrine and leucocytes and lymphocytes. The leucocytes soon fall a prey 

 to karyolysis and karyorhexis ; plasmorhexis is sometimes also observed. 

 When such changes are found one also sees organisatory processes in the 

 thrombus ; except in the thrombosised vessels where the intima is involved 

 in the organisatory process, one only finds the adventitia of all three layers 

 of the walls of the vessels affected. 



It is more densely nucleated around the vasa vasorum, even lymphatic 

 elements being accumulated in such places. An increase in elastic fibres 

 is not rare. During the appearance of these disturbances, the media is 

 not in any way affected. In strongly thrombosised vessels one finds 

 small nucleated foci in this portion of the wall. It was interesting to 

 demonstrate Diirck's* fibrilles by means of Weigert's iron haematoxylin 

 stainf ; they could be recognised running through the media, not unhke 

 telegraph wires. That these bristle-like fibrillae, which are so readily 

 damaged, are found intact shows that the walls of the vessels are affected 

 secondarily. 



The' basis of the foci of leucocytes is always a lymph space, although 

 the walls of the spaces are often hardly possible to demonstrate. Necrosis 



*H. Durck, Virchows Archiv, bd. 1.S9, 1907, Heft 1, page (;2. 



f Art. Weigert, "Nerveiifasevn," Enzyklopadie dev Mikroscopischoii Tcchnik, page 942, 



