178 LYMPHATIC SYSTEM. 



human body are very close to one another, our injection may 

 sometimes burst from one into another lying in contact with 

 it, without distending the cellular membrane which lies be- 

 tween them. A circumstance which I have seen happen even 

 on the mesentery of a turtle, where upon injecting the lacteal s 

 I have more than once made the mercury pass into the com- 

 mon veins ; but in all these cases, on a careful examination, 

 I found it was by rupture, as could readily be distinguished 

 in this animal, whose mesentery is extremely thin and trans- 

 parent. And that it actually was so, and not by a natural 

 passage, must be evident to every anatomist, who considers that 

 this is an experiment which does not always succeed on the 

 mesentery of the turtle, where, if there were natural passages, 

 or if the lacteals opened into the veins, the mercury would 

 probably run with great facility. 



And the very same circumstance which Dr. Meckel has ob- 

 served of a lymphatic gland has happened to me sometimes on 

 injecting these glands in diseased cases ; that is, I have filled 

 the common veins, and in some instances, where I looked for 

 it, I could distinguish the extravasation very readily, and 

 therefore concluded that in the other cases, where the veins 

 were filled, that it was also by an extravasation, though a 

 more obscure one. I should thence suspect that in Dr. 

 Mecke? s experiment, where he filled the common veins by in- 

 jecting into the lymphatic vessels of a diseased gland, a simi- 

 lar deception had taken place ; especially as the force applied 

 was considerable, he having used a column of mercury eighteen 

 inches high. 



And the supposition of the red veins opening into a lymphatic 

 gland appears improbable from an observation concerning the 

 structure of the glands, for which we are indebted to Dr. 

 Meckel himself, namely, that they are made of a convoluted 

 lymphatic vessel. 1 (See Note cxix*). Now to suppose a 

 lymphatic, which is a vessel given to absorb, should itself, even 

 when convoluted, have a common vein opening into it for absorp- 

 tion from its cavity, is not, I think, consistent with what we 

 know of nature's operations, who, to repeat the words of Glisson, 

 " Operam suam non ludit, neque quod actum est, agit denuo." 



Similar objections might be made to the other experiments 



1 Epist. ad Hallerum. 



