494 ARTHUR WILLIAM MEYER 



adventitia and the fibrous connective tissue which surrounded 

 and invaded the irregular degenerating mass also seemed to be 

 in process of degeneration. 



The distal ends of the veins in dogs and cats were practically 

 in the same condition although in some cases the original lumen 

 had become multiple by being encroached upon by the folded 

 degenerating media. It not infrequently contained some erythro- 

 cytes in a fair state of preservation and occasionally the 

 adventitia was very vascular where it was well-preserved. 

 Numerous small vessels were also found in the degenerating 

 media and not infrequently these communicated with the original 

 lumen to which they ran more or less parallel. No cellular 

 infiltration such as described by Haberda for man, was seen and 

 the whole picture was that of a degeneration rather than that 

 of an obliterative endarteritis. In fact, aside from the presence 

 of the small blood vessels in the connective tissue the impression 

 is usually that of a passive rather than of an active process and 

 it is difficult to see why a purely temporary complete substitu- 

 tion of fibrous connective tissue should occur in the veins only 

 to be absorbed as soon as formed. Such a complete substitution 

 of fibrous tissue for the vein may occur, to be sure, in animals 

 in which a true ligamentum teres hepatis is formed, but not, 

 of course, in those in which it never comes into existence because 

 of early resorption of the vein. Nevertheless, that a partial 

 transfonnation may take place even in these animals has already 

 been stated regarding the umbilical vein from a dog 91 hours old 

 a portion of which is represented under higher magnification 

 (figs. 6 and 7). Although this animal was less than four days 

 old the lumen of the peripheral portion of the vein which was 

 still attached to the umbilicus, is completely obliterated by a 

 slightly vascular connective tissue and the degenerating media 

 has become vascularized. The muscle fibers have lost their 

 outlines and specific staining reactions and are represented 

 by a degnerating mass containing irregular nuclei. Somewhat 

 farther centrally, i.e., nearer the liver, this vascularization is 

 much more evident as show^l in figure 7 and the fibrous con- 

 nective tissue filling the lumen has more the appearance of newly- 



