Diseases of the Heart and Organs of Circulation. 



295 



their normal function when put to the test. Water is poured in- 

 to one or other of the great arteries which arise from the ventri- 

 cles, the vessel being held vertically, and if it fails to descend into 

 the heart the valvular action is perfect. The auriculo-ventricular 

 valves may be equally tested by filling the ventricle and observing 

 whether there is a reflux into the auricle. 



The thickness of the walls of the heart varies in disease. 

 The auricular walls are invariably thin and flaccid except as above 

 noted with diminution of the auriculo-ventricular orifice. The 

 walls of the right and left ventricles differ in thickness in accord- 

 ance with the distance to which they have respectively to propel 

 the blood and the propulsive effort demanded. Thus the walls of 

 the right ventricle which is only called upon to propel the blood 

 through the lungs are only about J^ an inch in thickness and are 

 thinnest at their lower part. Those of the left ventricle which 

 have to send the blood to the most distant parts of the body are 

 from I to I J^ inches except at the lower part where they form 

 the apex of the heart, and are reduced to a tenuity resembling the 

 walls of the auricles. They are thickest at the median part, and 

 diminish slightly in an upward or downward direction. The bulk 

 of these walls is excessively muscular, the fibres arranged as an 

 elaborate double spiral and connected with a layer of white fi- 

 brous tissue placed in the interval between the auricles and ven- 

 tricles and surrounding the auriculo-ventricular openings and the 

 orifices by which the great arteries take their origin. It is at this 

 point, where the muscular fibres of the ventricles are connected 

 with the white fibrous rings, where rupture of the heart usually 

 takes place. 



The following measurements may be held to refer to medium 

 sized animals of the different kinds mentioned. 



