BY DR. BURDON-SANDERSON. 267 



so great that the aortic valves have not even time to close, or 

 under the various conditions in which these nerves are directly 

 or indirectly excited. From all these modifications, the effi- 

 cient causes of which are known and understood, lessons may 

 be learnt which may be applied directly at the bedside as aids 

 in the interpretation of analogous phenomena when they pre- 

 sent themselves in man. 



62. Study of the Action of the Valves in the Dead 

 Heart. Although this method forms no exception to the 

 general rule that little can be learnt in ph}*siology by teleo- 

 logical inferences from the properties of dead organs or tis- 

 sues, it is yet of great value to the student for the purpose of 

 illustrating the purely mechanical part of the action of the 

 heart. The heart of any mammalian animal may be used, that 

 of the pig being most suitable. The simplest method of imi- 

 tating the conditions which actually exist in the circulation, 

 consists in bringing one or other of the ventricles into commu- 

 nication with a reservoir placed at a sufficient height above it 

 by means of two flexible tubes. The most convenient form to 

 be given to the reservoir is that of a glass funnel, the stem of 

 which communicates by one of the flexible tubes with the aorta. 

 The other tube ends in a large glass canula, which is securety 

 tied into the ventricle near its apex ; its opposite end is fitted 

 to a glass syphon, the short leg of which dips into a funnel ; 

 the tube is guarded by a clip. The funnel and syphon having 

 been filled with water, and the clip closed, the apparatus is 

 ready. On opening the clip, water flows into the right ven- 

 tricle and distends it ; on closing it and compressing the ven- 

 tricle with the hand, its contents are forced upwards through 

 the aorta into the funnel, while the tricuspid valve is distended. 

 To observe the action of that valve, all that is necessary is to 

 cut away part of the wall of the right auricle. It is then seen 

 that, when the ventricle is squeezed, the liquid contained in it 

 tends to rush outwards by the auriculo-ventricular opening, 

 currying the valve with it. In a moment the curtains become 

 distended, meeting by their borders so as to form a tense mem- 

 branous dome, which projects into the auricle. The time which 

 intervenes between the commencement of the compression and 

 the tightening of the valve varies according to the vigor of the 

 contractions, the quantity of blood contained in the ventricle, 

 and the previous position of the valve, but must always be ap- 

 preciable. It corresponds to the pros systolic period previously 

 referred to. All these facts are learnt much more impressively 

 by introducing the index finger into the right auricle of a large 

 animal. In the horse this can be done easily by an opening 

 of such size that the finger is tightly grasped by it. The valve 

 bulges out as a tense membranous dome into the auricle at the 

 moment of auricular contraction. In observing the action of 



