286 THE BLOODVESSELS, BY C. J. EBERTH. 



researches of Iwanoff * and myself, of a delicate network of 

 fine fibrils, composed of the processes of stellate cells lying 

 directly upon the vascular wall. Each of these cells consists 

 of a large elongated nucleus, invested by an extremely delicate 

 layer of protoplasm. 



CHRONSCZCZEWSKY! observed, in capillaries which had been treated 

 with nitrate of silver, the cells detached from their connections, and 

 at the same time the external wall of the capillary prolonged over the 

 hiatus. However little evidence there may be against the presence of 

 a tunica adventitia in the capillaries of other organs, I must still remark 

 that such observations as the above, for reasons that I cannot here 

 discuss, are not always conclusive. 



Between the capillaries of the hyaloid of the Frog isolated 

 stellate cells occur, with round nuclei and delicate protoplasm, 

 branching off into many processes which often anastomose with 

 the processes of the cells of the tunica adventitia. Towards the 

 small arteries and veins the pericapillary plexus becomes con- 

 stantly closer, and soon in its stead there appears a delicate 

 transversely folded and nucleated membrane, which is sometimes 

 elevated in the form of small vesicles. 



The general structure of these parts renders it scarcely 

 probable that, as Iwanoff admits, the capillary sheath con- 

 stitutes a lymph space .} Numerous examinations of the 

 tunica adventitia of the larger hyaloid vessels, treated with 

 nitrate of silver, and undertaken with the view of detecting the 

 indications of cells in it, have led, in all instances, only to 

 negative results. 



A similar nucleated membrane forms the outermost covering 

 of the larger-sized capillaries, and of the arteries and veins of 



* Medizinisches Centralblatt, No. 9, 1868. 



t Virchow's Archiv, Bandxv., p. 172, 1866. 



J In my first treatise I described the capillaries of the pecten in the eye 

 of the bird as possessing a delicate double-contoured tunica adventitia re- 

 sembling the structureless membrane of certain gland tubes. More recently 

 I have satisfied myself, from transverse sections of the pecten, that the 

 apparent tunica adventitia is only the hyaloid membrane which invests the 

 whole of the pecten, and from its exactly following the course of the 

 vessels, gives, when seen on the flat, the illusory appearance of a complete 

 tunica adventitia. 



