VEIN. 



1391 



to contain veins, and that the venous textures 

 become more strongly marked as the parts 

 become more mature ; and that veins but 

 little removed in size from capillaries, differ 

 from them by the addition of structures 

 exactly similar in nature to those which 

 larger veins possess in a greater amount. 



The development of capillaries has been ob- 

 served, principally, by Schwann* in the tails 

 of young tadpoles, and the germinal mem- 

 brane of an incubated hen's egg, by Kollikerf , 

 in the tails of batrachian larvae generally, and 

 by Paget^ in the foetal membranes of sheep. 

 Their accounts, which my own observations 

 on the tails of batrachian larvae entirely con- 

 firm, all substantially agree. 



On subjecting the tail of a very young tad- 

 pole to microscopical observation, and viewing 

 it with an object glass of a quarter of an inch 

 focal distance, it will^be seen that the vessels 

 possess all the characteristics of very fine capil- 

 laries, that is, they possess a delicate, perfectly 

 homogeneous membrane, with nuclei adhering 

 here and there to its internal surface. The 

 two great arterial and venous trunks are 

 elongated posteriorly, as the larvae grow, by 

 throwing out prolongations, which, by joining 

 the embryonic cells accumulated about the 

 extremity of the chorda dorsalis, inosculate 

 with them so as to form a continuous cavity. 

 The first lateral vessels of the tail, which 

 have the form of simple arcs going from artery 

 to vein, are formed by the junction of pro- 

 longations, from the caudal artery and vein, 

 with certain elongated or stellate cells in the 

 substance of the tail. From these vessels, 

 which constitute what may be called the pri- 

 mary arches, are thrown out projections which, 

 by inosculating in an exactly similar way with 

 neighbouring stellate cells, form secondary 

 capillary arches; and thus the capillary net- 

 work continually extends itself in proportion 

 as the tail gets longer and- broader, and at the 

 same time becomes more dense by the forma- 

 tion of new vessels between th 

 meshes. 



Such are the general appearances seen in 

 the tail of any of the batrachian larvae. These, 

 however, Schwann does not consider so con- 

 clusive as the appearances in the germinal 

 membrane of a hen's egg. He says that when 

 the germinal membrane of a hen's egg which 

 has been subjected to thirty-six hours' incuba- 

 tion, is placed under the microscope, and the 

 area pellucida examined with a magnifying 

 power of 450, the capillary vessels are readily 

 distinguished in it. In some situations they 

 are perfect, and connected with the larger 

 vessel, some are of irregular calibre, having 

 bulgings here and there where two or three 

 channels meet, the intervening portions vary- 

 ing in size from that of a fibre of yellow 

 fibrous tis ue to the full capillary diameter, 

 and permeable to blood or not. 



* Microscopical Researches, translated for the 

 Sydenham Society, by Henry Smith. 



f Annales des Sciences Katurelles. August, 1846. 



j Supplement to Miiller's Elements of Physiology, 

 by Drs. Baly and Kirkes. 



e primitive 



In addition to these capillaries, which form 

 a network of channels of irregular calibre, 

 and give off blind branches, some separate 

 irregular corpuscles are seen which are not 

 connected with the vascular network. These 

 bodies send off blind processes, of various 

 forms, in different directions ; in other words, 

 they are stellate cells. They have a reddish- 

 yellow colour, like that of the capillaries of 

 bone, which circumstance alone would be suf- 

 ficient to make it probable that they are the 

 primary cells of capillaries in process of forma- 

 tion ; and this probability becomes a certainty 

 when we perceive that some of these same 

 stellate cells are already connected with the 

 true capillaries, forming with them a common 

 cavity. This is Schwann's description. Of 

 its correctness I cannot speak from my own 

 observation, but of the correctness and ex- 

 treme truthfulness of Kolliker's account of 

 the same process in the tails of young batra- 

 chia I can, from my own observations, con- 

 fidently speak : indeed he has left nothing to 

 be added. 



MORBID ANATOMY OF VEINS. 



Veins are subject to a variety of morbid 

 changes, which are naturally incident to blood 

 vessels of their particular organisation and 

 functions, occasioning a remarkable contrast 

 in their pathology with that of arteries. 



Thus veins are much more subject to diffuse 

 inflammation than arteries, and the products 

 of their inflammation being carried in the blood 

 to the heart, are conveyed all over the body ; 

 they moreover offer peculiar facilities for the 

 introduction of morbid materials into the cir- 

 culation, and from both these circumstances 

 wide-spread and diffuse disease is the result 

 conditions which have no parallel as the conse- 

 quence of arterial disease. Again, an injury to a 

 vein, such as a punctured wound, is followed by 

 cicatrization; and any dilatation of its tube 

 interferes only partially with its functions; 

 whereas in an artery, from the vigorous and 

 pulsating character of the circulation in it, a 

 wound is only to be healed by obliteration of 

 the vessel, and any dilatation of it causes 

 an aneurism a progressive and destructive 

 disease. 



From the time of Hippocrates, some of the 

 diseases of veins varix and haemorrhoids 

 have been recognised ; but it was not till John 

 Hunter, in 1793, published his paper on the 

 diseases of veins in the " Transactions of a 

 Society for the Improvement of Medical and 

 Chirurgical Knowledge," that any light was 

 thrown upon that most important of these 

 diseases phlebitis. 



Since then the subject has received a large 

 share of attention at the hands of some of our 

 most distinguished pathologists : and Hodg- 

 son, Travers, Breschet, Bovillaud, Ribers, A^r- 

 nott, Lee, and hosts of others, have all added 

 their quota towards its elucidation. 



The diseases of veins divide themselves into 

 phlebitis, with which may be considered the 

 effects of wounds and ligatures; varix and 



