LYMPHATIC SYSTEM. 175 



Lower has related another experiment which has frequently 

 been quoted by writers on the dropsy ; that is, where he tied 

 the jugular veins of a dog, and the dog's head became dropsical. 

 Now were this an experiment which always succeeded it would 

 be more decisive, for when the whole cava was tied, no part of 

 the blood being able to return, all the vessels below, not only 

 the small veins, but the small arteries, must have been extremely 

 distended. Whereas in this experiment no such thing would 

 take place, because the jugular veins so frequently communicate 

 with other vessels, that there would still be a regress allowed 

 to the blood ; if the neck therefore became oedematous, it would 

 appear more likely to have been occasioned by the ligature on 

 the veins. But what shows that there must have been some 

 fallacy in Lower's experiment is, that these veins have since been 

 frequently tied without an oedema being produced, or any signs 

 of extravasated lymph. Thus, in not one of the experiments 

 which I made on these veins in living dogs (as related in the 

 first part of these Experimental Inquiries) was this effect ever 

 produced ; and Baron Van Swieten tied up both the jugular 

 veins, and though he kept the dog four days afterwards, did 

 not observe him any way incommoded. 1 In one dog I even 

 cut out both the external jugulars, and kept him near a twelve- 

 month without observing the least symptom of dropsy. I 

 should therefore suppose, that in Lower's experiment, not only 

 the veins, but the lymphatic vessels which lie near them, had 

 been tied; in which case the lymphatics 'would burst and oc- 

 casion these symptoms. But in my experiment I took care 

 to separate the vein from the lymphatics. 



These arguments, therefore, in favour of absorption being 

 performed by the common veins, which are brought from ex- 

 periments where ligatures were made on large vessels, seem 

 likewise to be liable to fallacy. 



A fifth argument is taken from the structure of the placenta, 

 where it has been concluded there are no lymphatics ; and yet 

 there must be absorption, and not a communication of the 



1 Comment in Boer. Aph. 170, p. 266. 



coagulated blood ; see Note xui, p. 24. I long ago deposited pre- 

 parations illustrating this fact in the museum of the Army Medical 

 Department at Chatham. 



