168 LYMPHATIC SYSTEM, 



different cavities of the body, as the pericardium, pleura, peri- 

 toneum, tunica vaginalis, &c., get into these cavities merely by 

 transudation, is to suppose, not only that the small vessels in 

 contact with these membranes have inorganized pores, but also 

 that these membranes themselves have the same just opposite 

 to those of the vessels. Now if we admit inorganized pores at 

 one part of those membranes, we must admit them in all parts, 

 and in the same degree ; but as the blood-vessels are circular, 

 and touch those membranes only by a small part of the circle, 

 the parts touched by the vessels must be smaller than the 

 interstices between the vessels, and the lymph must have fewer 

 chances in favour of its leaking from the vessels into the cavities, 

 than of its oozing again from these cavities into the interstices 

 between the vessels or into the cellular membrane ; so that, if 

 these membranes admitted of transudation, there would be no 

 such thing as a partial dropsy, for the water would run out at 

 one part of the pleura, pericardium, peritoneum, &c., as fast as 

 it ran in by the other, and an anasarca would always accompany 

 an ascites ; which not being a fact leads us to believe, that 

 those membranes do not admit of transudation in living bodies, 

 and that the fluids get into them not by inorganical, but by 

 organized passages. 



Thirdly. To prove more satisfactorily that these fluids are 

 not filtrated from the blood merely by inorganical transudation, 

 let us recollect the experiments related in the last chapter con- 

 cerning the properties of those fluids, which we found varied 

 in different circumstances of health. For, in inflammatory 

 affections of the parts from which they were secreted, they 

 assumed the appearance of the coagulable lymph of the blood, 

 and formed a tough jelly ; in animals in health they formed a 

 jelly of a weaker nature ; and in dropsical cases they were al- 

 most a mere water, without the property of coagulation. Now 

 if these fluids be so variable in their properties, it is manifest 

 that the passages secreting them cannot be always unalterably 

 the same, or inorganized; since at one time we find them secreting 

 one fluid, and at another time secreting another; especially as we 

 sometimes find them secreting a fluid very different from the 

 blood, viz. pus. Which pus being found in cavities without any 

 ulcer or erosion (see Note LXXIT), we must conclude it formed 

 by something more than a mere filtration; for we cannot suppose 



