CIRCULATION 



239 



of any of the various forms of cardiograph, one of the simplest 

 consisting of a receiving and recording tambour connected by 

 means of a tube (fig. 114). (Practical Physiology.) 



The form of the trace varies according to the part of the 

 heart upon which the button is placed, but it has the character 

 shown in fig. 115 if the button is upon the cardiac impulse. 



At the moment of ventricular systole the lever is suddenly 

 thrown up to a certain level (a to 6). From this point it 

 suddenly falls slightly (b .to c), but is maintained during the 

 ventricular systole above the abscissa (c to d). At the end of 

 the ventricular systole, as the heart falls away from the chest 

 wall, the lever falls to its original level (d to e). In many 

 tracings a small rise of the lever may be seen just before the 

 great upstroke. This corresponds to the contraction of the 

 auricles. 



In various diseases of the heart the cardiogram is materially 



FIG. 115. Cardiographic Trace, a to d, ventricular contraction, 

 modified. Hence it is important to have a clear conception 

 of the various parts of the trace. 



The elucidation of the various parts of the cardiogram is 

 only possible after careful study of the other changes in the 

 heart during the cycle. 



6. Changes in the Intraeardiae Pressure. 



These can be studied only in the lower animals. 



The most common way of determining the pressure in a 

 cavity is to connect it to a vertical tube and to see to what 

 height the fluid in the cavity is raised. If such a method be 

 applied to the ventricles of the heart, the blood in the tube 

 undergoes such sudden and enormous changes in level that 

 it is impossible to get accurate results. 



The same objection applies to the method of connecting the 

 heart with a U tube filled with mercury. When this is done 

 the changes in pressure are so sudden and so extensive that 



