174 LYMPHATIC SYSTEM. 



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for than by absorption, we are left in doubt whether in those 

 instances, where anatomists observed such a fluid in the veins 

 of the mesentery, it had been owing, not to those veins absorb- 

 ing it, but to their receiving it from the arteries. All the 

 serum of the body being now and then as white as milk. 1 



A third argument produced in support of absorption by the 

 common veins is taken from the structure of the penis, whose 

 veins arise from its cells ; which cells, however, are now allowed 

 to be particular organizations, and very different from those of 

 the cellular membrane, and the blood is believed not to be 

 absorbed, but to be impelled from these cells into those veins ; 

 and the argument is now given up even by some of those who 

 were once the most strenuous in its favour. 2 It need not 

 therefore be here dwelt upon. 



Ligatures, or compression on the large veins, have been 

 considered as furnishing a fourth argument in favour of these 

 veins arising from cavities, and doing the office of absorption. 

 Thus the swelling of the legs in pregnant women, and in cases 

 where tumours have been seen near the veins, has been ex- 

 plained from the uterus in the one case, and the tumours in 

 the other, occasioning such compression, as to prevent the re- 

 turn of the venous blood. But there are two circumstances 

 which make this argument far from being satisfactory. First, 

 the lymphatic vessels run near such veins, and it is doubtful 

 whether the lymph may not be retained in th6 limbs more 

 by the compression of these vessels than by that of the veins. 

 Secondly, the compression of a vein may, by stopping the 

 return of the blood, not only distend the small veins, but the 

 small arteries, and the exhalants may be so dilated, or so 

 stimulated, as to secrete more fluid than they did naturally. 

 In this way, perhaps, the ligature which Dr. Lower made on 

 the cava inferior of a dog occasioned the ascites. 3 An experi- 

 ment which I have repeated, but my subject did not live so 

 long as his, for mine died in half an hour, and had only a 

 very little water in the abdomen (LXXXJ). 



1 Instances of which may be seen in the first part of these Exp. Inquiries. 



2 See Professor Monro's State of Facts. 3 De Corde, cap. ii, p. 112. 



(LXXXI.) (Edema of the lower limbs is much more frequently con- 

 nected than is commonly supposed with obstruction of the veins by 



