ADVANCED DEMONSTRATIONS 393 



c.c. of blood must have passed through the heart in the minute. Thus 

 the output 



2000 - 

 = _=25c.c. 



The output in mammals is reckoned to be about -0012 of the body 

 weight per sec. 



Stewart's Method of Determining Output of Heart. In the anaesthet- 

 ised dog, a cannula is introduced through the jugular vein into the 

 superior vena cava, and connected with a burette containing 1-5 per 

 cent. NaCl. A short cannula provided with a rubber tube and clip 

 is introduced into one femoral artery A. The other femoral, B, is 

 exposed, placed on electrodes with sheet indiarubber beneath. The 

 electrodes are connected with a Wheatstone bridge arrangement, 

 through which weak induction shocks are passed from coil. A telephone 

 is introduced in the bridge and the latter is balanced. 



A sample of blood is drawn from A and defibrinated. A measured 

 quantity of the salt solution is then run into the vena cava superior 

 for 10", the time being noted by a stop-watch; the pulse is counted 

 at the same time. As soon as the salt solution reaches B the resistance 

 alters and the telephone sounds. 



The time at which this occurs after the injection gives the jugular to 

 femoral circulation time. While the telephone is sounding a sample is 

 drawn from A. The specific resistance of the two samples is deter- 

 mined by the telephone Wheatsone bridge method (see Lehfeldt's 

 Physical Chemistry, p. 62). The samples are placed in small U -tubes 

 immersed in running water, and provided with platinum electrodes. 

 The quantity of 1 -5 per cent, salt solution is measured, which must be 

 added to the first sample to make its resistance equal to the second 

 sample. This determination gives us the means of estimating the 

 extent to which the injected solution has been mixed with blood in 

 the heart, and therefore, knowing the quantity of solution run in, 

 we can calculate the output in the given time. Lastly, from the pulse 

 rate, we can calculate the output per second. 



Stewart finds the output to be '0015 to *003 of body weight 

 per sec. 



The Influence of the Pericardium in Preventing Over-distension of 

 the Heart. A cannula is placed in the superior vena cava of a dead 

 cat, and the inferior vena cava and pulmonary artery are ligatured. 



Fluid is run into the superior vena cava from a burette from a height 

 of about 100 mm. The amount of fluid which enters the heart is 

 estimated. After removing the pericardium, twice as much fluid will 

 enter the right heart under the same pressure, and the heart will 



