16 VASCULOGENESIS IN THE CAT 



Blutkorperchen ohne lokomotorische Eigenbewegung gebraucht werden 

 kann, dartiber will ich hier nicht weiter sprechen. Wir haben bloss 

 damit zu rechnen, dass Helly den Durchtritt roter Blutkorperchen (auch 

 Froschblutkorperchen) durch die unversehrte Wand der venosen Milz- 

 capillaren gesehen hat iind dass er hierin ein Hauptargument ftir die 

 Lehre vom geschlossenen Kreislauf in der Milz erblickt. 



To summarize, the injection method gives us extravasation. 

 This has a positive value when physiologic or subnormal pressures 

 are used. It proves the permeabihty of the vessel wall. For 

 the structure of that wall, whether complete or incomplete ana- 

 tomically, and especially for the ultimate morphologic fact, the 

 form and relation of its constituent elements, it is valueless and 

 these questions must be settled by direct observation, and not 

 by indirect conjecture founded upon physical or physiological 

 experiment. To quote Mollier again, referring to the question 

 of open or closed circulation in the spleen: 



Welcher Art diese Untersuchungen sein miissen, ergibt sich einmal 

 aus dem Resultat der Injektionsversuche, welche lehren, das dieselben 

 immer wieder sowohl zugunstfn der einen wie der anderen Anschau- 

 ung Beweismaterial geliefert haben. Sie sind also wohl nicht imstande, 

 diese Frage zu entscheiden, und es ist besser, von ihnen zuniichst ganz 

 abziisehen.-" 



His own brilliant solution of the problem of the structure of 

 the sinus wall, is a ground of confidence to those who hold that 

 structural problems are best approached by anatomic methods. 

 In view of the complexity of structure and function in living 

 beings, it will probably continue to be held the part of wisdom 

 to determine then- relation empirically and not attempt to deduce 

 structure from the physical or even the physiological properties 

 of organs and tissues. 



The positive findings of the injection method, that there are 

 in the embryo continuous vascular channels, that these channels 

 have ends, and their walls are very pervious, can therefore be 

 accepted for they are corroborated by other methods of investi- 

 gation. The negative propositions that have been advanced 

 by users of this method, that the embryo has only continuous 

 endothelium, that its only source is from sprouts, that the ends 

 of vessels do not communicate with tissue spaces, are not proved 



" Loc. cit. 



