THE CIRCULATION OF THE BLOOD 677 



dog, one from a human patient with a systolic mitral murmur, due to escape 

 of blood through the imperfect valve during systole, and a third in which there 

 was a musical murmur during diastole, due to incompetence of the aortic valves. 



The second sound, a sharp one, is caused by the sudden tension put on the 

 aortic valves as they are shut by the aortic pressure when the ventricle begins 

 to relax. The first sound, of a softer and more prolonged character, appears to be 

 due to two causes ; one, the closure of the auriculo-ventricular valves, the other the 

 muscular contraction, since it can be heard in the excised, empty heart. The 

 pitch of this second element is the same as that of the resonance of the ear passage, 

 which exaggerates the vibrations which correspond to its own period. 



RELATION OF ACTIVITY TO OXYGEN CONSUMPTION 



Some facts relating to this question have been already given (page 612). 

 The work of Rohde (1912) and of Rohde and Nagasaki (1913) requires a little 

 more detail. 



In order to be able to control the conditions, the isolated perfused heart (cat 

 or rabbit) was used in the method described in 1910, with the improvement of 

 placing the whole in a thermostat. The object was to determine the relation 

 between the activity and the chemical changes, including the consumption of 

 oxygen and of glucose, the production of carbon dioxide and of other end products. 



The first result is identical with that of A. V. Hill, already mentioned, on 

 skeletal muscle, namely, that there is a direct proportionality between the oxygen 

 consumption and the pressure developed in isometric contraction, in which the 

 volume of the heart does not change. An important point is that, although the 

 pulse rate is considerably lower at 15 than at 36, the oxygen consumption per 

 millimetre pressure developed is the same, within the limits of experimental error, 

 namely, 427-436 x 10~ 7 c.c. of oxygen. This fact of the absence of temperature 

 effect on the conversion of chemical to mechanical energy is, no doubt, an 

 important one from the point of view of energetics ; what it means is not yet 

 clear, although the surface energy as a " limiting factor " is indicated. 



From the work of Zuntz and his co-workers on the whole animal we know 

 that we can convert the oxygen consumed into its equivalent of oxidised food-stuff, 

 in the proportion of calories developed. This was found to hold in the heart. 

 The ratio of pressure developed to calories produced by oxidation was the same, 

 whether glucose with a respiratory quotient of 0'98, or the "reserve stuff" of the 

 heart itself, with a respiratory quotient of 0-80, was consumed. 



In short, the ratio of the chemical energy of oxidation, or calories, to the 

 amount of pressure developed is a constant number. 



To obtain further insight into the mechanism of the energy change, experiments 

 were made in which the heart was placed under abnormal conditions, narcotics, 

 want of oxygen, the influence of muscarine, of veratrine, etc. It was found that 

 the heart muscle worked less efficiently ; that is, less pressure was developed in 

 proportion to the oxygen consumed. As a first step towards the analysis of these 

 results, the behaviour of the heart as regards different food-stuffs was investigated. 

 When glucose was present in the circulating Ringer's solution, the carbohydrate 

 was consumed along with certain reserve materials present in the cells themselves. 

 As to the chemical nature of these " reserve stuffs " we have little information. 

 There is no evidence that protein is consumed in muscular contraction. In fact, 

 the experiments of Athanasiu and Gradinesco (1912) seem to show that it is not. 

 They kept the excised heart of a frog beating normally for thirty-three days, 

 giving about 360,000 beats, in Ringer's solution containing glucose and oxygen 

 only, in addition to the salts. Any store of protein, if used for energy purposes, 

 must have been exhausted early in the experiment. If any was used, it could 

 only have been the minimal amount required for repair of the machine. See also 

 the work of Evans and Matsuoka (1915) as regards the relation of oxygen con- 

 sumption to the production of energy. 



Rohde found that the effect of adding atropine, or adrenaline, or retarding 

 oxidation by potassium cyanide, is to increase the consumption of glucose and 



