Changes in Transplanted Blood Vessels. 113 



either of the same or of different species, and continue, for a certain 

 period of time at least, to fulfil all physiological requirements. 

 Various changes may be noted in the gross appearances of the 

 transplanted segments, depending on the vessel transplanted, the 

 site of transplantation, and the animal into which the implantation 

 takes place, whether of the same or different species, closely or 

 distantly related. 



A segment of a rabbit's aorta was placed in the carotid of a 

 dog, by the Carrel method of suture, and removed at the end of 

 seventy days. The mechanical function of the vessel was perfect. 

 The lumen was moderately dilated, and the walls slightly thinned. 

 Upon microscopical examination, however, the normal structure 

 of the transplanted segment had almost entirely disappeared. 

 The intima had disappeared, being replaced by a layer of hyalin 

 fibrin and blood ; the muscular elements had either disappeared or 

 been greatly reduced in number, while the various layers had 

 been the seat of many fine hemorrhages, which showed as small 

 masses of hyalin fibrin into which new connective tissue had pene- 

 trated. New fibrous tissue had replaced the whole structure of the 

 vessel wall to a marked degree. The striking change, however, 

 was the absolute disappearance of all the elastic tissue in the trans- 

 planted segment. Sections stained by Weigert's elastic tissue 

 stain showed no elastic tissue in the piece of rabbit's aorta, 

 while that in the carotid of the canine host was normal and ran 

 up to the line of suture, where it stopped abruptly. 



The entire disappearance of elastic tissue has not been ob- 

 served in segments transplanted from one animal to another of 

 the same species. A segment of a dog's aorta implanted in the 

 aorta of a second dog, and examined at the end of seventy days, 

 shows a very slight and scarcely appreciable diminution in the 

 amount of elastic tissue in the transplanted segment, the slight 

 loss being in the finer fibrils. There is no regeneration of elastic 

 tissue, as there is a well defined wedge of connective tissue, with- 

 out elastic elements, between the sutured ends of the cut vessels. 

 The muscular and connective tissue layers are well preserved ; 

 the endothelium is missing in some places. 



The more widely separated the species of animals used, the 

 more rapid and complete is the disappearance of the elastic tissue. 



