736 THE HABVEIAN ORATION. 



attainment; for many years ago — in 1784, in fact — and three years 

 before the appearance of Mascagni's splendid work, with similar 

 figures and histories of similar experiments ('Vasorum Lymphati- 

 corum Historia et Iconographia/ 1787), the continuity of the 

 lacteal radicles upon the walls of the intestine with the 'lymph- 

 paths' — to borrow a word of later coinage — in the mesenteric 

 glands, and finally, after passing through successive lines of these 

 apparently solid structures, with the thoracic duct itself, had been 

 demonstrated by Sheldon, then Professor of Anatomy in our Royal 

 Academy of Arts. These are his words (from p. 49 of his work, 

 'Of the absorbent System,' 17 84), .describing his plate No. 5 : 'In 

 the fifth plate of this work, upon a portion of human jejunum from 

 an adult female subject, seventeen lacteal vessels are injected with 

 quicksilver, by inserting pipes into them upon the intestine. They 

 were remarkably large and varicose in this subject, and as the quick- 

 silver was poured into the lymphatic injec ting-tube to fill these 

 vessels, it frequently ran out in a full stream by the jugular vein, 

 which was opened. This circumstance rendered it evident that the 

 mercury had passed through the whole course of the lacteals and 

 thoracic duct, and had penetrated even into the venous system. It 

 is, I believe, the only instance in which the thoracic duct has been 

 injected from the lacteals on the intestines ^.' 



Sheldon's first plate, I may add, when compared with his letter- 

 press on p. 37, appears to show that what he calls 'ampullulae' were 

 really Peyerian glands, and that he had repeatedly seen these gland s 



^ I have some pleasure in pointing out that by making a reference to the plates of 

 the venerable Professor Arnold, fasc. i. tab. i. fig. 2, 1838, it maybe seen that the 

 quicksilver injection could sometimes give as correct results as the * silver method ' of 

 modern microscopy for the detection of lymphatics by their epithelium. The figure I 

 refer to shows the fourth ventricle plexus without, the velum interpositum on the 

 contrary with, lymphatics injected with quicksilver. The use of the silver method has 

 enabled me to prove that this representation is correct : abundance of choroidal villi 

 can be procured — and very beautiful objects they are when treated with 0-25 per cent, 

 solution of nitrate of silver — from the plexus in the fourth ventricle, but no lymphatic 

 vessels. These can be shown from the velum interpositum by the use of the same 

 reagent. The use of quicksilver as an injection-substance has not always led to as 

 happy results as in the instance just given. Not to specify other cases, it is curious 

 to note that the penetration of this material into the parieto-splanchnic ganglion of 

 the Lamellibranchiata when thus employed by the skilful Italian anatomist, Poli, 

 and its distributing itself thence into the nerves given off from it by displacement of 

 their granular neurine, seduced him into supposing these structures to constitute a 

 lymphatic system, * cistemam lacteam et vasorum lactiferorum surculos.' See * Tes- 

 tacea Utriusque Siciliae,' tom. i. p. 39, 1791. 



