230 Prof. ¥/. Jones on the Caudal Heart of the Eel. [Jan. 9_, 



II. The Caudal Heart of the Eel a Lymphatic Heart.— Effect of 

 the force with which the lymph- stream is propelled therefrom 

 on the flow of blood in the Vein into which the heart opens. 

 — Explanation of the appearance of blood propelled in successive 

 drops, as if from the heart, along the Caudal Vein. — Influence 

 which the force of the lymph-stream from the heart exerts in 

 accelerating and promoting the flow of blood in the Caudal Vein/' 

 By Thomas Whahton Jones, F.R.S., Professor of Ophthalmic 

 Medicine and Surgery in University College, London, Ophthalmic 

 Surgeon to the Hospital, &c. Received November 26, 1867. 



(Abstract.) 



To explain the true nature of the phenomenon of drops of blood pro- 

 pelled in rapid succession, as if from the caudal heart, along the caudal 

 vein, — to prove thereby that the caudal heart belongs, not to the blood- 

 vascular system, but to the lymphatic system, — and to inquire into the in- 

 fluence which the force of the lymph-stream from the caudal heart exerts in 

 accelerating and promoting the flow of blood in the caudal vein, constitute 

 the object of this paper. 



The great caudal vein of the eel is formed by the junction of two trunks, a 

 larger and a smaller. It is into the smaller trunk, near its junction with the 

 larger, that the caudal heart opens. At the opening, there is a valve which 

 prevents regurgitation of the lymph back from the vein into the heart. 



When by the contraction of the heart the lymph is propelled into the 

 vein, the flow of blood from that vessel into the great caudal trunk is 

 interrupted by the force of the lymph-stream. From the place where the 

 heart opens into the vein to the junction of the latter with the caudal 

 trunk, colourless lymph thus replaces red blood; whilst in the caudal 

 trunk itself, the lymph, still under the influence of the heart's force, so far 

 displaces the blood as to flow in a colourless stream on one side of the 

 vessel for some distance, distinct from and unmingled with the blood- 

 stream from the lower part of the vein and its lateral branches. 



During the diastole of the heart, the stream of lymph into the vein in- 

 termitting, the flow of blood from that vessel into the great trunk of the 

 caudal vein again takes place. No sooner, however, has a small quantity 

 of blood entered than, systole of the heart ensuing, the stream of lymph 

 thereby propelled into the vein, drives the small quantity of blood before 

 it into the great caudal venous trunk, whilst it at the same time arrests, as 

 before, the flow of blood into the great caudal vein from its tributary vessel. 



Through the medium of the stream of lymph propelled into the great 

 caudal vein at each stroke of the caudal heart, an impetus is communicated 

 to the column of blood in that vessel, which we can see has the effect of acce- 

 lerating and promoting its onward flow to the blood-heart of the animal. 

 W e thus see that the caudal heart of the eel is a lymphatic heart, its 



