1 824.] of Dilatation of the Heart. 1 83 



power which enables the ventricles to dilate themselves. Pray 

 what is the nature of the action of an elastic body ? Mr. John 

 Hunter thus defines it : " The action of elasticity is continual, 

 and its immediate effects are produced whenever the resistance 

 is removed ; by which it may be distinguished from other 

 powers." * From our definition, we learn that the action of an 

 elastic body is permanent, and that as soon as the resisting 

 power which retains it in a forced position is removed, that it 

 immediately regains its natural state of rest. In order to the 

 elucidation of our problem, we shall admit the body of the left 

 ventricle of the heart to be possessed of an elastic property. As 

 the systole of the ventricle throws the elastic property into a 

 forced position, and as the ventricle remains for some time after 

 its last systole in a comparative state of collapse, we have only 

 to do away with the influence of the power which retains it 

 during that period in that state, and the elastic property will 

 instantly restore itself to its natural position. Before we set 

 about releasing it from its constrained situation, we shall inquire 

 into the nature of the power which we have to contend with. 

 Asa state of relaxation in a muscular fibre succeeds the state of 

 contraction, it follows that the action of the muscular fibres of 

 the walls of the ventricle cannot be the cause of the confinement 

 of the elastic property in its unnatural position, for we admit 

 contraction to be the last motion of the ventricle. The resisting 

 power then must arise from the propulsion of a portion of the 

 blood into the aorta from the cavity of the ventricle by its sys- 

 tole, without its being able (by its elasticity or active power of 

 dilatation) to draw its wonted supply in return from the auricle, 

 on account of the latter being itself deprived of its usual supply. 

 Therefore, as the elastic property endeavours by its reaction to 

 regain its natural state of rest, a tendency to form a vacuum in 

 the cavity of the ventricle must be the result, which effectually 

 retains the elastic property in its constrained position. Now if 

 we can establish a communication between the cavity of the 

 ventricle and the exterior air, it is evident that we shall do 

 away with the tendency to a vacuum, and consequently with the 

 resistance offered to the reaction of the elastic property. Such 

 a communication is easily established without, doing any injury 

 to the walls of the ventricle, by opening one of the pulmonary 

 veins, near their junction with the auricle. In the narration of 

 our experimental investigation, we are informed that after such 

 an expedient was had recourse to, that no such phenomenon as 

 dilatation of the ventricle was remarked. Therefore if we can 

 depend on the correctness of the observations during the above 

 experiments, and if observations under such circumstances can 

 be relied on, we must conclude the active power of dilatation, or 



* On the Blood. 



