HYDE: COLLATERAL CIRCULATION IN THE CAT. 171 



The vessels that appeared in the ligated area and anasto- 

 mosed between veins that carry blood directly and indirectly to 

 afferent paths may owe their origin to local pressure. We 

 should expect that under this condition there would be a greater 

 flow in certain directions, causing an enlargement of the paths 

 of those cliannels, and that this in turn would influence, with 

 the rise of pressure, a thickening of the walls of the smallest 

 vessels. This would be in harmony wath the laws formulated 

 bv Thoma,* in his study of the development of blood-vessels. 



When the anastomosing network of vessels of the ligrated 

 postcava and its tributaries increased, the pressure lowered, 

 and the flow in that direction became more rapid. In conse- 

 quence of this the caliber of the azygos and its tributaries in- 

 creased. 



The results of these experiments prove that in all cases where 

 tlie blood-flow through the postcava has been hemmed by patho- 

 logical growths that compressed the vessel, or, where it is nec- 

 essary, due to accident or operation, to obstruct the flow through 

 it, the normal activities of the body will not be materially im- 

 paired if the paths leading to the azygos and through it to the 

 heart are not interrupted. 



In cases of atrophic cirrhosis of the liver, where the blood- 

 flow from the vena porta is prevented by compression of the 

 blood-vessels in the liver, collateral circulation was first estab- 

 lished by Talma, t He caused adhesion between the abdominal 

 wall, the liver, spleen, and omentum. The blood reached the 

 postcava partly from anastomosing networks of vessels devel- 

 oped in the adhesive region, the hypogastric, 'and femoral. Sur- 

 vival would, I should think, be possible even if under such 

 circumstances the postcava in the region of the liver were so 

 compressed by the disease as to stop the flow" through it, pro- 

 vided the passage through the azygos and its tributaries in the 

 abdominal region were kept open. 



*Thoma: Untersuchungen fiber die Histogenese und Histomechanik des Ge- 

 fassystems. Stuttgart, 1893. 



tS. Talma chirurgische Oeflfnung neuer Seitenbahnen fiir das Blut der Vena 

 Porta. Berliner Klinische Wochenschrift, 1898. 



