518 PHYSIOLOGY CHAP. 



The results arrived at by Gley and Camus can be summed up 

 in a few words : 



(a) The left splanchnic nerve contains dilator fibres and also 

 constrictor fibres to the receptaculum. As the electrical excitation 

 of the nerve trunk almost always produces depressor effects, we 

 must conclude either that the constrictor fibres are not very 

 numerous in the part of the nerve which is stimulated, or that 

 they are much less excitable than the dilator fibres. 



(6) The motor nerves to the thoracic duct run in the thoracic 

 part of the sympathetic chain. Here also there are dilator and 

 constrictor fibres, and the activity of the former outweighs that of 

 the latter. 



(c) It is also possible, rerlexly, by exciting a sensory nerve to 

 determine dilator effects upon the receptaculum and thoracic 

 duct. If, e.g., one sciatic is ligatured, alternate constriction and 

 dilatation will be observed in place of the former constant tonus. 

 On exciting the central end of a divided sciatic, there is invariably 

 a dilator effect. On the other hand, asphyxia on cessation of 

 artificial respiration determines contraction of the thoracic duct 

 similar to that exhibited by the stomach, bladder, uterus, bile 

 duct, etc. 



These observations show the importance of the muscle cells 

 and motor nerves of the lymphatic vessels, in so far as they are 

 capable of altering their lumen, and can thus facilitate or hinder the 

 centripetal movement of the lymph. If these active vascular 

 movements were more energetic, rhythmical, and peristaltic or 

 progressive from the branches to the lymphatic trunks, it is 

 evident in view of the function of the manv valves with which 



h 



the lymphatic system is furnished that they would have the 

 same effect as the heart-beats, and would represent a form of 

 propulsion adequate to account for the lymphatic circulation. 

 But this view has no experimental basis, nor does it harmonise 

 with the theory of the venous circulation, which depends essentially 

 upon the vis a tergo developed by the cardiac rhythm. 



According to Ludwig the lymphatic circulation depends 

 essentially on the vis a tergo due to the pressure on the lymph 

 that fills the pareuchymatoiis lymph spaces, which in its turn 

 depends on the pressure under which the blood circulates in the 

 capillaries. Thus the lymph circulation is also, in last resort, the 

 effect of the force of the heart. The lymph represents a transudate 

 from the blood through the fine membrane constituted by the 

 capillary walls, by a process of filtration which depends on the 

 difference of pressure between the blood circulating in the 

 capillaries and the lymph poured out into the spaces. Tiiis theory 

 will be analysed below. For the moment it is enough to say that 

 it is correct, in so far as it assumes the lymph circulation to be 

 due to the vis a tergo caused by the pressure on the lymph in the 



