BLOOD VESSELS 473 



H. FLOW OF BLOOD THROUGH DIFFERENT ORGANS. 



This may be studied — 



(A) In lower animals in the following ways : — (1) By 

 use of the Stromuhr (p. 466) ; (2) by the plethysmo- 

 graph method. This consists in enclosing the organ 

 in a plethysmograph, and, while the blood is flowing, 

 clamping the vein for a ver}- brief period. The organ 

 expands according to the amount of blood which flows in, 

 and the increased volume gives a measure of the blood flow. 

 The vein is again undamped, and the observation may be 

 repeated. 



In lower animals it has been found that the flow 

 of blood through different organs when measured per 100 

 grm. of organ per minute is very different, in the 

 stomach only about 21 c.c, in the kidney, 150 c.c, and in 

 the thyreoid no less than .5 60 c.c. 



(3) The time taken by the blood to pass through an 

 organ may be determined by injecting some electrolyte, 

 e.g. NaCl solution, into the artery, and measurmg the 

 electrical conductivity of the blood in the vein by means of a 

 Wheatstone's bridge. When the salt solution reaches the 

 vein this is increased. 



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