viii BLOOD -STREAM: MOVEMENT IN VESSELS 261 



The follow 



researches : 



The following are some of the data derived from Dogiel's 



The velocity of the blood-flow, which is essentially a function 

 of the resistances in that part of the circulation to which the 

 haemodromometer is applied, must rise and fall w r ith the increase 

 and decrease of resistance. It is probable that the mere manipu- 

 lation necessary for inserting the cannula in the artery is sufficient 

 to 'produce relaxation of it .and its principal branches, thereby 

 determining an abormal rise of current velocity, which soon falls 

 again in consequence of the recovery of normal vascular tone. 



Dogiel further showed that there may be a compensatory rise 

 in current velocity in the carotid on exciting the splanchnic nerve ; 

 this has no direct action on the carotid region, but since it 

 provokes contraction of the vessels in the abdominal viscera, it 

 increases resistance in a remote vascular region of considerable 

 extent. He also observed, when using two stromuhrs on the same 

 animal, that the velocity in the carotid and the femoral arteries 

 may vary now in the same, now in the opposite sense. This shows 

 the great adaptability of capacity in the various vascular regions, 

 the mechanism of which will be studied in the next chapter. 



Tschuewsky (1903), using Hiirthle's recording stromuhr, has 

 made a great many observations on dogs, upon the mean velocity 

 of the blood in the different arteries, and under various experimental 

 conditions. The following table gives the average of his 

 results : 



From this table it appears that the velocity is normally much 

 lower in the crural artery than in the carotid, and that after 



