310 GENERAL ANATOMY. 



if they are filled and distended in the subject, the matter which 

 is introduced into them, is rejected. 



Vital irritability or contractility* is no less evident in them: 

 although Mascagni and several others have denied it. If they 

 be exposed to the air in a living subject, they manifestly con- 

 tract; if the thoracic duct or any other lymphatic vessel be 

 punctured after being tied, the liquid issues by jets, like the 

 blood which comes from a vein, while after death, it only 

 escapes in a sheet over the lips of the wound. It is true that 

 mechanical or chemical irritations do not produce movements 

 similar to those of the muscles, but we must observe that irri- 

 tability varies according to the organs. 



We know nothing concerning their sensibility, and little 

 about their force of formation. 



470. The lymphatic vessels contain the chyle and lymph 

 [79]; they convey these humours from their radicles to their 

 trunk, which is very well proved by the arrangement of their 

 valves, which permits the fluid to flow in that direction, but 

 prevents it in an opposite one; by the effects of the ligature, 

 below which they swell while they empty themselves above; 

 and by the valves which are placed at their insertion in the 

 veins. The passage of the liquids through them is slow and 

 uniform, that is to say, they do not present any pulsation. 



Darwin, Thilow and others, in order to explain the rapidity 

 of certain secretions, have admitted a retrograde movement of 

 the humours in the lymphatic vessels: in such a manner, for 

 instance, that the liquid absorbed by the parietes of the sto- 

 mach should be directly conveyed by the lymphatic vessels, 

 and by means of their communications to the kidneys, and 

 hence to the bladder. This would be to admit that the valves 

 do not present a very great obstacle to the retrograde motion 

 of the liquids. But it is certain, on the contrary, that the 

 valves oppose an insurmountable obstacle to the return of the 

 liquids; and moreover, observations and direct experiments 

 cause us to discover in the urinary passages substances intro- 



* Schreger, de Irritabilltate vasomm lymphaticorurn. Lips. 1789. 



