Transplantation of blood-vessels
It is possible to perform two kinds of vascular transplantations，uni-terminal transplantation and bi-terminal transplantation.The uni-terminal transplantation consists in grafting one extremity of a vessel on to another part of the vascular system，and includes many different varieties.The main result of a uni-terminal transplantation is to change the quality of the blood circulating through a certain vessel and to modify its pressure.If the peripheral end of the external jugular vein is united to the central end of the carotid artery，the vein becomes filled with red blood and its pressure is augmented，whilst the pressure of the artery diminishes.The vessels readily adapt themselves to these modifications.An augmentation of the pressure in the carotid artery，pro-duces a thickening of its walls.After several months，hypertrophy[36]of the muscular coat and sclerosis[37]of the intima arise.If on the other hand，the pressure of the carotid[38]artery is diminished by anastomosing it with a large venous system，such as the superficial veins of the neck，its wall becomes thinner，and hypertrophy of the intima is produced.When an arterial circulation is established through a vein，the wall of the latter rapidly responds to the change by becoming thicker.When the carotid vein and the external jugular vein are united，the wall of the jugular vein becomes much thicker，although its pressure is less than ordinary arterial pressure.When the wall of the vein has to bear still more pressure，as，for instance，when the central end of the carotid artery is united to the peripheral end of the inferior thyroid vein，the reaction of the venous wall is very much greater.The lumen of the vein diminishes and the wall shows an enormous sclerosis.
These uni-terminal transplantations were used in order to modify the circulation of certain vascular regions.Thus it was possible to produce a reversion of the circulation in the posterior limb by performing a cross anastomosis of the femoral artery and vein.In many instances we have modified the circulation of the veins of the neck and head as well as of the veins of certain organs.The union of the carotid artery and of the external jugular vein allowed the blood to pass from the carotid into the superficial veins of the neck and of the head，whereupon the latter pulsated like arteries.It was also possible to diminish the pressure of the upper carotid by uniting its central end to the central end of the jugular[39]vein[40]，and thereby the arterial blood was made to return immediately to the heart through this vein.In various other experiments I was able to reverse the direction of the circulation of an organ，such as the thyroid，in which case the thyroid vein was united to the carotid and the thyroid artery to the jugular.
It is possible that some of the numerous operations per-formed by means of uni-terminal transplantation of blood vessels may some day be of practical use.So far these operations have above all shown how sensitive the walls of the vessels are to changes in the pressure of the blood，and how readily，by becoming thinner or thicker，they adapt themselves to these modifications.
The bi-terminal transplantation consists in interposing a segment of a vessel between the ends of another vessel.This transplantation can be carried out in various ways，according as the segment is interposed between the cut ends of an artery or vein，or between two different regions of the circulatory system，or，again，between a serous membrane and a vein.If the transplanted segment is from the same animal，or from another animal of the same kind，or from a different kind of animal，the transplantations are autoplastic[41]，homoplastic or heteroplastic respectively.
The first arterial transplantation was performed in 1896 by Jaboulay.He thought that this method could be applied to the treatment of aneurisms，but the anastomoses were im-perfect and in each case thrombosis of the vascular segment occurred.Nine years later Hoepfner successfully performed the transplantation of segments of arteries by using the method of Payr.In a remarkable series of experiments he demonstrated the possibility of transplanting arteries without any obliteration resulting therefrom.In 1905，at the University of Chicago，with the help of Dr.Guthrie，I took up this study.In a large number of experiments conducted subsequently at the Rockefeller Institute，the results of this method were studied in greater detail.Segments of the carotid artery or aorta of a dog and a cat were transplanted on to the same animal，another animal of the same species，and an animal of a different species.The vessels used were either fresh or had been preserved in cold storage.These operations performed with fresh vessels of proper caliber invariably showed positive results.The circulation continued in a normal manner and at the end of several months the transplanted segment usually presented the same appearance as the normal vessel.
In the case of autoplastic transplantations there was no change in the appearance of the vessel，which preserved its normal diameter and its elasticity.The only trace left by the operation was two whitish transverse lines，which were visible on the endothelial surface of the wall of the vessel.The histological examination likewise showed that the wall of the vessel had undergone no change.
In homoplastic transplantations the appearance of the vessel also remained normal.When the vessel was examined on the living animal six months or more after the operation it was usually impossible to locate the transplanted segment.E-ven in cases in which the vessel had been preserved for several weeks in cold storage the results were the same.But a histological[42]examination made three months or more after the operation often showed that the histological constitution of the wall had become modified.In some cases the wall had remained normal，but in the majority of cases the muscular fibres had completely disappeared and the intima[43]had thickened.The elastic fibres of the media always remained in a normal condition，even after several years.Hitherto it has not been possible to recognize before operating the animals that may undergo an exchange of vascular segments without suffering degeneration of the muscular fibres，and those whose muscular fibres would，after such an exchange，completely degenerate.
In heteroplastic transplantations the results were different.Segments of the carotid from dogs were grafted on to the aorta of a cat or the segments of the aorta of a cat on to the carotids of dogs.Also segments of human aortas were transplanted on to the aorta or carotid of dogs.Obliteration often occurred in cases where human vessels were transplanted on to other human beings，but this obliteration may possibly be attributed to secondary causes，as the vessels employed had been preserved in cold storage.In nearly all cases in which the carotid of a dog had been transplanted on to the aorta of a cat the results were positive and the circulation remained normal.The clinical results were observed during a period of time varying from several days to more than four years.The anatomical evolution of the heterologous[44]vessels is different from the evolution of the autologous and ho-mologous vessels.Their caliber becomes progressively larger，but this augmentation of the diameter does not augment indefinitely and never results in the formation of aneurisms[45].Similarly the wall becomes thinner.The histological examination showed that，during the weeks and the months following the transplantation，not only the muscular fibres had degenerated but the elastic framework had also completely disappeared.Thus the wall only consisted of connective tissue.A dog，which in 1907 had undergone the resection of the abdominal aorta and the transplantation of a segment of a human popliteal[46]artery，died four years after the operation.The vascular segment was slightly dilated and the anastomoses were normal.But the wall contained neither muscular nor elastic fibres.The same results were observed after the arteries of a cat or of a rabbit were transplanted on to a dog.The lesions consisted in the progressive disappearance of the elastic and muscular elements of the wall，of an augmentation of interstitial connective tissue and of a thickening of the intima.But the resistance of this fi-brous wall was sufficient and the segment of the artery was able to take the place of an artery during several years.In these arterial transplantations fresh segments，or such as had been preserved in cold storage，were used.The clinical results were identical in both cases，that is to say，when the period of preservation in cold storage had not exceeded two or three months.Vessels preserved in formalin[47]or by means of a system of thorough drying were also used.In the latter experiments the wall of the vessel，which was devitalized，had become regenerated at the expense of its host.
The transplantation of veins was attempted for the first time by Glückin 1898，but the segment of the jugular vein which he transplanted on to the carotid artery of a dog became quickly obliterated.Exner attempted to perform the same experiments，as did also Hoepner and Goyanes.The results of these operations，however，were always negative.In 1905 I succeeded with Guthrie in transplanting segments of the jugular[48]veins of a dog on to the carotid[49]artery.Later on I was able to graft segments of the vena cava on to the abdominal aorta or on to the vena cava of dogs or cats.Finally I succeeded in performing the same operation on the thoracic aorta of a dog.The upper part of the descending aorta of a fox-terrier having been cut transversely，a segment of the jugular vein of a large dog was interposed between the extremities of the vessel.The animal remained in an excellent condition.More than two years after the operation he died of poliomyelitis[50]，which at that time was epidemic in dogs.The autopsy showed that the venous segment was not dilated and that the valves were in the same condition as at the time of the operation.The muscular fibres of the wall had disappeared，but the diameter of the vessel was practically the same as that of the neighbouring parts of the aorta.
I have performed many venous transplantations，both autoplastic and homoplastic.In the case of the autoplastic transplantations the vein immediately underwent important anatomic modifications.The wall became thicker while the lumen became slightly dilated；but aneurism[51]never oc-curred.On the contrary，the vein adapted itself to its arterial function，and responded to the pressure of the blood by thickening its wall.This thickening was mainly produced by an augmentation of the connective tissue of the adventitia[52]and of the intima.Sometimes，too，the number of muscular fibres increased.Four months after the transplantation of the segment of the jugular on to the carotid of a dog，I removed a small piece of the wall and sutured the wound.The histological examination showed a large increase of the connective tissue of the adventitia and of the connective tissue of the intima，but the muscular fibres were normal.Twelve months later the venous segment was examined again.It was found that the wall had become still thicker and that all the muscular fibres had degenerated.In the homoplastic transplantations the clinical evolution showed the same results，but all the muscular fibres disappeared more or less rapidly.These experiments served to demonstrate，therefore，that the segment of a vein，notwithstanding the thinness of its wall，may perform the function of an artery.From a practical point of view it is possible to replace segments of arteries by sections of veins.On human beings this operation would be easier than the transplantation of arteries，as it is always possible to find on the patient himself a segment of vein suitable for transplantation.
In still other experiments a piece of the wall of an artery，such as the aorta or carotid，was extirpated and replaced by a fragment of vein or peritoneum.In some cases the entire section of a vessel was removed and replaced by a tube of peritoneum[53]，but in this case thrombosis of the tube occurred in a few days.When a piece of the wall was resected and replaced by a patch of perito-neumor vein，the results were always positive.The adaptation of the pieces of peritoneum or vein to their new conditions was so perfect，that in less than two years after the operation the wall of the vessel was almost normal，although it showed a slight thickening at the point where the operation had been performed.The exterior appearance of the abdominal aorta of a dog，on to which a patch of peritoneum had been grafted，was in no wise modi-fied，although the wall was composed of a different tissue.It possessed the same thickness and appearance as the adjoining normal portion of the wall.By a kind of mimetism[54]the connective cells of the peritoneum had taken on the aspect of muscular fibres.In spite of the absence of muscular and elastic fibres，such as those possessed by the normal aorta，the new wall supported the pressure of the blood without dilating.Aneurism was never produced unless there was bacteriological infection.The only way in which I succeeded in provoking fusiform aneurisms[55]was by transplanting tissues which had been infected.I also succeeded in repairing the wall of an artery with the aid of foreign organic and inorganic substances.A portion of the anterior[56]wall of the abdominal aorta of a dog was replaced by a piece of rubber.Fifteen months after the operation the function of the aorta had not become modified and its lumen was normal.A thick layer of connective tissue had formed on the inside and outside of the venous piece.In other experiments glass and metal tubes covered with paraffin were introduced into the thoracic aorta of the dog.The blood did not coagulate as long as the wall of the artery was not ulcerated.A dog whose thoracic aorta contained a piece of glass remained in perfect health for 90 days and finally died of an ulceration[57]of the aorta.These experiments showed that the presence of foreign bodies in the lumen[58]of a vessel does not necessarily produce a thrombus，as was formerly believed.This observation caused a simplification of the technique of the transfusion of blood to human beings.
These various experiments on blood-vessels demonstrated that arterial or venous transplantations could be performed with safety when a proper technique was used.It was of little importance whether the muscular fibres were preserved or not，as the vascular wall adapted itself to the pressure，and no dilatation occurred.Autoplastic and homoplastic transplantations of arteries and veins may，therefore，be adopted in surgical practice for those cases in which it is necessary to reestablish the continuity of an artery.