184 



PHYSIOLOGY 



CHAP. 



coni arteriosi (lying beneath the orifices of the aorta and pulmonary 

 arteries) ; these present a smooth surface, destitute of reticular 

 trabeculae, and provided with stout bundles of longitudinal 

 muscles. 



The far greater bulk of the walls of the left ventricle, in 

 comparison with those of the right, is especially due to the 

 presence of a third layer of muscle fibres, which can be isolated 

 with nitric acid; this dissolves the tendinous and connective 

 tissues, making it possible to separate the inner and outer coats of 

 muscle fibres. In this way an intermediate layer of fibres can be 

 isolated which are almost circular in direction and form a some- 

 what conical mass ; these do not end in tendons, but wind round 



upon themselves, and belong ex- 

 clusively to the left ventricle 

 (Krehl : Fig. 54). 



No less interesting than the 

 changes of external form are the 

 systolic changes within the ven- 

 tricular cavities. To form an 

 adequate notion of these, it is 

 necessary to fix and harden two 

 human hearts, one in a state of 

 total systole, the other, as nearly 

 as possible of the same size, in a 

 state of maximum diastole (Krehl's 

 method). 



Fi<;. .">4. Middle, layer of muscular libres, 

 destitute of tendons, from left ventricle of 

 human heart, after removing internal and 



To obtain the dead heart fixed in 



external layers. The form of the heart is diastole, it must either not have entered 



schematically indicated. A the natural , ,. . , . 



size. (Krehl ) the state ot rigor mortis, or must already 



have passed out of it. After carefully 



removing the heart from the thorax, all the great vessels must be made 

 water-tight (by means of corks introduced into their lumen), with the excep- 

 tion of the pulmonary vein and the vena cava superior, into which two 

 glass tubes of the same calibre as that of the vessels must be introduced, and 

 fixed by ligatures. Through these tubes the heart is filled with water under 

 a hydrostatic pressure of 50-100 mm. of mercury. The water enters by the 

 great veins into the auricles, and by the aorta into the coronary arteries, out 

 of which it filters slowly through the cardiac walls. The heart is thus 

 thrown into acute diastole, which is more pronounced than in life, and 

 is left 6-8 hours in this state. It is then fixed with 96 per cent alcohol, 

 which is passed through it for 3 to 4 hours under the same pressure as that 

 used for the water. To complete the hardening, absolute is substituted for 

 the dilute alcohol, without any further pressure. 



Fixation in systole is effected by Hesse's heat method. The freshly 

 extracted heart is placed for an hour in a solution of potassium bichromate 

 at 52 C., which throws it into a state of pronounced systole. 



Total systole of the human heart can only be demonstrated on the heart 

 of a subject who has died suddenly, at the maximum of rigor mortis. 



Dissociation of the cardiac fibres is easy- after treatment with ordinary 

 nitric acid. This acid, however, shortens the muscle fibres, and throws the 

 heart into more or less complete systole. In order to dissect out the heart 



