1^2 THE SALAMANDER 



The course of the blood through the heart Is briefly as follows. 

 The left auricle fills before the right. The systolic rhythm com- 

 mences with the sinus venosus, which empties itself completely into 

 the right auricle, and, as a result, the inter-auricular septum is pushed 

 over into the left auricle, which accordingly commences to discharge 

 its contents into the ventricle. The two auricles then contract almost 

 simultaneously, the left leading ever so slightly, and thus the blood 

 from the left auricle passes into the proximal or left-hand side of the 

 ventricle, and that from the right into the central cavity and distal 

 or right-hand side. The first blood to leave the ventricle is that 

 from the right auricle, then a mixture from both right and left 

 auricles, and finally that from the left auricle only. Now the resis- 

 tance offered by the several vessels leaving the truncus is not identical 

 in each case. The greatest resistance is offered by the carotid arch, by 

 virtue of its labyrinth, and the least by the pulmonary arch. As 

 therefore, the systole spreads on the ventricle, the first blood to 

 leave would enter the latter vessel, and the last would go to the head 

 via the internal carotid artery. The difference in pressure between 

 the pulmonary and systemic arches must be very slight since they are 

 connected by a perforate ductus Botalli, but the actual capacity of the 

 pulmonary system is relatively small, and hence it speedily fills and 

 allows the greater part of the blood to flow into the other two arches. 



Noble's experimental results, which are simply that none of the 

 ink injected into the pulmonary vein ever entered the pulmonary- 

 artery, are thus easily explained without involving the septum bulbi 

 at all. There is another important feature to be noted which seems 

 to have been overlooked by previous writers, namely, that as shown 

 on p. 274 the bucco-pharynx is as intimately concerned with respira- 

 tion in the Salamander as the lung, and this region, although sup- 

 plied mainly by the pulmonary arch, returns most of its blood into 

 the jugular veins and hence into the r/^/z/ auricle, so that although the 

 blood of the left side of the heart is purely oxygenated blood, that of 

 the right side must also contain a considerable amount of oxygen. 

 Thus, by virtue of this and the systolic rhythm, the spongy ventricle 

 and the resistance of the carotid labyrinth, the Salamander possesses 



transillumination from the bulb of an ophthalmoscope lamp placed under the heart. He 

 observed no perceptible difference in the colour of the blood in the three arches, and also 

 found that Indian ink injected into the pulmonary vein vi^as distributed simultaneously 

 and equally to each of the three arterial arches. He therefore concluded that the septum 

 bulbi was not responsible for any selective distribution of the two kinds of blood, and 

 in fact went further, and claimed that the blood from the right and left auricles does not 

 remain distinct in its subsequent passage through the remaining portions of the heart. 



