284 CIRCULATORY SYSTEM. 



strongly advocated by several anatomists and physiologists, for 

 the following reasons: 1. That the known roots of the lym- 

 phatic system have an area much superior to that of the trunks 

 in which they terminate. 2. That substances introduced into 

 certain lymphatics by absorption or injection, have been found 

 in the contiguous veins. 3. That a ligature upon the thoracic 

 duct produced death only after ten or fifteen days, and then the 

 articles which had been absorbed by the intestines, were found 

 in the blood. 4. .And that injections had proved this commu- 

 nication. 



Notwithstanding the well known fact of injections, under cer- 

 tain circumstances, passing from the arteries into the lympha- 

 tics, some anatomists of modern date have hesitated in admit- 

 ting a direct communication. M. Meckel has, indeed, rejected 

 the notion entirely, on the ground that the fluid contained in the 

 trunks of the absorbents is always the same as one finds at their 

 commencement. For example, the lymphatics coming from the 

 liver contain a fluid like bile; those which come from the mammae 

 contain a fluid like milk; those which come from parts suffering 

 from an extravasation of blood contain a sanguineous fluid; the 

 bronchial glands are coloured by the black pigment brought to 

 them from the lungs; poisonous matter, as that of the small-pox 

 or venereal, irritates and inflames the lymphatics that lie in the 

 course of its introduction into the system. For these reasons it 

 would appear to him, that the arteries do not continue themselves 

 into the lymphatics as they do into the veins. The observations 

 of M. Lauth seem to have proved the point, that some of the 

 lymphatics take their origin from the internal surface of the ar- 

 teries; and it may be through them that injections have been 

 forced from one system into the other. In the case of the liver 

 of a child, I have injected its absorbents very successfully from 

 the arteries. 



The coats of the lymphatics generally are too thin and trans- 

 parent for an investigation of their structure ; but as those of the 

 thoracic duct are sufficiently large for the purpose, one may 

 estimate the structure of other trunks by it. It is thus ascer- 

 tained that they consist of two coats, an internal and an exter- 

 nal one. 



The external coat is somewhat irregular on its surface, from 

 its connexion with the adjacent cellular substance ; and has a 



