vii MECHANICS OF THE HEAET 211 



forward by Thebesius (1708). According to this theory the 

 coronary arteries empty during systole and expand in diastole, 

 either because in systole the orifices of the coronary vessels are 

 closed by the raising of the semilunar valves and their application 

 to the walls of the sinus Valsalvae, or because the finer ramifica- 

 tions and capillaries of the coronary vessels are closed or drawn 

 together by the contraction of the myocardium. 



The first argument was refuted by Lancisi (1728) in opposition 

 to Thebesius, and again, with more cogent reasoning, by Hyrtl 

 against Briicke, and it is, in the light of all that is known about 

 the mechanism of the semilunar valves, entirely erroneous. 

 Neither Hyrtl nor Ceradini, however, found any valid objection to 

 the second argument, which is to-day regarded as established by 

 the experiments of Klug and Rebate!, and the more recent work 

 of Porter and Hyde. Klug succeeded in the living animal in 

 ligaturing one heart in systole and another in diastole. On 

 microscopic examination he found that the superficial vessels were 

 full of blood in the first heart, while the deeper ones were almost 

 empty : in the second, all the coronary vessels were turgid. 

 Rebatel, using Chauveau's haemodromograph (see next chapter), 

 succeeded in obtaining a tracing of the pressure and velocity of 

 flow in the coronary arteries of the horse. He found that pressure 

 and velocity increase in the first period of systole ; that at a 

 second period, pressure increases and velocity decreases until it 

 becomes negative (arrest and recession of blood into the coronary 

 vessels) ; finally, that at the beginning of diastole there is accelera- 

 tion of velocity without increase of pressure. Porter was able to 

 convince himself by an admirable method, in the dog, that the 

 intramuscular branches of the coronary vessels were compressed 

 and emptied by the contraction of the myocardium, and that this 

 systolic evacuation assisted the streaming of the blood through the 

 walls of the heart when the myocardium relaxed, owing to the 

 diminished resistance offered by the slack and empty vessels to the 

 blood-stream. Lastly, Hyde studied the effects of the various 

 distensions of the ventricular cavities on the isolated cat's heart, 

 by suffusing blood through the coronary vessels at constant 

 pressure. He determined that whether the heart was at rest or 

 beating, the flow of blood diminished when the heart was more 

 extended, i.e. when circulation in the coronary arteries was 

 impeded. 



But even if the automatic regulation of the heart, in so far as 

 systole impedes the circulation in the coronary arteries by com- 

 pressing them, while diastole facilitates the filling of the coronaries, 

 be accepted, it does not necessarily follow, as assumed by Briicke, 

 that there is in diastole a kind of erection of the cardiac walls 

 which tends to produce a negative pressure in the cavity, and to 

 facilitate its filling. It is true that Bonders and Albini claim, 



