14 VASCULOGENESIS IN THE CAT 



be attended with sensations, even emotions, on the part of the 

 observer. Yet it cannot thereby be proved that the vessels end 

 blindly; and we ought not to assunie, because of the deUcacy of 

 embryonic structures that their physical properties are different 

 in kind, or obey other general laws of stress and strain than larger 

 tubes which are more accessible to examination. 



But while the results of injection demonstrate the permeabil- 

 ity of the vessel wall, as do in hfe the passage of cells and fluids, 

 they do not afford us the opportunity of ascertaining the structure 

 of the wall or the nature of its orifices. They simply give us the 

 concept of permeability, which it is not permissible, without fur- 

 ther grounds, to translate into porosity. Every fact of extrava- 

 sation can be admitted and the integrity of a completely closed 

 vessel wall still be maintained if we introduce the concept of a 

 structureless (invisible) membrane, the resistance of which to 

 pressure is practically nil. 



HelJy"^ has shown this with admirable clearness in his interest- 

 ing work upon the vessels of the spleen. He confirmed previous 

 observations of the passage of injections through the vessel walls, 

 whether solutions, suspensions, colloidal masses, or foreign blood 

 corpuscles were used. He further washed out the red blood cor- 

 puscles from the pulp spaces by saUne irrigation, and caused their 

 numbers in the pulp to increase by retrograde injection (obstruc- 

 tion of the splenic vein) and finally in sections of 5 /i observed 

 both erythrocytes and leucocytes in passage through the walls of 

 the sinuses. Yet he considered the wall complete. 



Was zuniichst den Widerstand aniangt, welchen die Gefasswand dem 

 Durchtritte fester und flussiger Bestandteile entgegenzusetzen vermag, 

 so ist ersichtlich, dass derselbe bei den veiiiiscn Capilhiren nur sehr geriiig, 

 an gewissen Stellen der Wand iiberhaupt fast gleicli null ist; gleicht sie 

 doch, von der Flache betrachtet, sehr einem Gitter, dessen Lucken viel- 

 fach gross genug sind, um ein rotes Blutkorperchen ohne jede merk- 

 liche Formverandcrung durchtreten zulassen. Dem zwischen beiden 

 Bestandteilen des Gitters, — den inneren, parallel zur Langsachse des 

 Gefasses angeordneten, stabformigen EiKlothclzelleii und den ausseren, 

 quer um dasselbe verlaufenden Kreisfaseni, — befindliche unmessbar 

 diinncn strukturlose Hiiutchen kann wohl kein irgend nennenswerter 

 Einfiuss im Sinne einer Behindcruiis der l^iapcdese zugeschrieben wer- 

 den und dies umso weniger, als das gcdachtc Hautchen sehr liinfiillig ist 



" 1903, Arch. f. mikr. Anat., IJil. 01, |). 245. 



