vii MECHANICS OF THE HEAHT 215 



katabolic products, to assimilate oxygen and nutrient juices from 

 the environment. For this purpose the anisotropous substance seeks 

 to acquire the largest possible superficies, i.e. it expands. Yerworn 

 does not deny that this expansive movement (i.e. relaxation) is 

 assisted by numerous extrinsic factors, e.g. the tension of tendons 

 and fascia, etc., but he still attributes a not inconsiderable function 

 to the expansive activity proper of the muscle fibres. Albrecht 

 extended to the heart the idea which Yerworn had formulated for 

 muscles in general. He accordingly defines diastolic activity as a 

 functional necessity of recuperation. 



Other authors, on the contrary, ascribe the active character of 

 diastole to the elastic tissue contained in the myocardium. Krehl 

 appears to have adopted this hypothesis. He holds that there are 

 many elastic fibres beneath the endocardium, surrouuding the 

 muscle bundles of the internal layers, which may be thrown into 

 tension during systole, and react in diastole by dilating the 

 cavities of the heart. The elastic lamellae which extend from the 

 semilunar valves passing under the origin of the aorta into the 

 interior of the muscles may produce the same effect. Lastly, he 

 believes that the root of the aorta, deeply implanted, and always 

 distended under high pressure during the energetic systolic 

 diminution of the base of the heart, must be deformed ; so that at 

 the commencement of diastole, when it recovers its position of 

 equilibrium, the pressure must involve .a distension of the soft 

 muscles. This last idea is a new form of Gaule's hypothesis, as 

 already refuted. In any case, Krehl's propositions, as a whole, 

 leave us uncertain whether the dilator reaction of the heart, at 

 the commencement of diastole, is to be ascribed to the elastic 

 tissue or to the cardiac muscle. The former is, however, absolutely 

 put out of court by certain very important facts adduced by 

 Stefani, which go to determine the physiological character of the 

 active diastole. 



VIII. In a previous paragraph we referred to the changes in 

 total volume of the heart, during the several periods of its activity. 

 We said that it diminished during systole, at the termination of 

 which meiocardia occurs, i.e. the maximal diminution of the heart's 

 volume ; and that it increases during perisystole until it attains 

 the maximal volume, or auxocardia, at the commencement of 

 presystole. 



After our first experiments in 1871 (in which, to estimate 

 the changes in volume of the heart, we employed the pericardial 

 cavity filled with milk) Franck and Stefani (1877) were the first 

 who adopted the method of the pericardial fistula for curarised 

 dogs, kept alive by artificial respiration tracings of the oscillations 

 of the total volume of the heart (cardiac plethysmogram) being 

 recorded on a rotating drum. This is easy enough with simple air 

 transmission, i.e. by connecting up the cannula applied to the 



