250 A Study of the Structural Unit of the Liver 
of the vessels was very irregular, at points forming rosettes in which 
narrow and dilated vessels alternated. Loeb concludes that not only did 
the entire vascular system develop without any circulation of blood, but 
also without any intravascular pressure, for had there been one, the capil- 
laries which were developed should have been found distended. Further- 
more, it is shown that the capillary buds grow independently of blood- 
pressure. “ Die mechanischen Ursachen fiir das Wachsthum der Gefass- 
winde sind deshalb nicht im Gefasslumen zu suchen, sondern in allen 
oder einzelen Zellen der Gefiaisswinde und die Abgabe von Aesten ist 
bestimmt durch inner, Ursachen in den Zellen der Gefasswande oder durch 
Reizursachen, die von der Umgebung ausgehend, diese Zellen treffen, 
ahnlich wie im Falle der Stolonenbildung von Hydroidpolypen.” * 
It is also seen from Thoma’s own illustration (Fig. 3, d), that capil- 
laries in which the pressure must be equal degenerate or multiply, as the 
case may be. In the transformation of Fig. 3 into Fig. 4, Thoma’s first 
law on the rapidity of the circulation must have directed all of these 
changes. In fact, Thoma’s hypothesis, on the budding of capillary cells, 
is not based upon intracapillary pressure alone, but also “vom Stoff- 
wechsel der umgebenden Gewebe, ” which can easily be harmonized with 
Loeb’s “ Reizursachen, die von der Umgebung ausgehend, diese Zellen 
treffen.” 
In reality we can only state definitely that with the new formation of 
tissue new blood-vessels may grow into it, for all new tissue does not 
have blood vessels. Thoma’s first two laws define much better and ex- 
press more clearly the ideas relating to the question brought together by 
Roux ™ in his Inaugural Dissertation. To be sure, it is all functional 
adaptation, for the circulating blood arranges the irregular capillary 
anlage for a uniform circulation. 
One would think that if the favored blood vessel dilates, a number of 
them would soon connect the arteries with the veins, and thus do away 
with the capillaries entirely. Thoma states that the reason why this does 
not take place is to be found in the great relative distance between the 
primary artery and vein, which is continued in their subsequent tree-like 
growth. From our present conceptions, it would appear, however, that 
occasionally an intervening capillary would dilate a little above the nor- 
mal, and, being favored, would gradually become larger and larger. In 
fact, Brissaund and Sabourin have asserted that such anastomoses are 
quite common between the terminal portal and hepatic veins in many 
== Ibayeo ly Cas 10h Galle 
> Roux, Ges. Abhandl., I, p. 19. 
