86 



Chapter VI 



outflow of blood (i.e. the pressure in the aorta) being greater than 

 the force of contraction, it was performing a series of approximately 

 isometric movements. At the point where the tracing changes its 

 character the resistance to the outflow was abolished by introducing 

 a tube through the wall of the left auricle into the left ventricle 

 so that now the heart could drive its blood up the tube at each 

 contraction. In the first period the heart bore some resemblance to 

 an enlarged heart with incompetent semi-lunar valves : this is 

 characterised by the rapid pulse and the failure to produce effective 

 contractions. In the isotonic period the rhythm had returned to 



FIG. 51. 



its normal rate and the contractions were well marked. The oxygen 

 consumption in the first period was '174 c.c. per minute, in the 

 second "169. Another point of interest arises in that the slightly 

 greater oxygen consumption was associated with a reduced blood- 

 flow. In the isometric period the blood passing through the coronary 

 system was 1*9 c.c. per minute, in the isotonic it was 2'6." 



The other point to which we would refer is the apparently much 

 greater irregularity of the figures for carbonic acid than of those for 

 oxygen. This irregularity is due to a number of causes, such for 

 instance as the solubility of the gas in the blood and any change in 

 the acidity (hydrogen ion concentration) of the heart itself, for it 



