456 THE SOLIDS. 



certain that, as a general rule, the Malpighian bodies remain unaffected, 

 both in structure and in their office of secreting the watery constituents 

 of the urine, until the whole of the disintegrated epithelium has been 

 washed out of the tubes. Of this there are two proofs ; the first is the 

 fact of a very long convoluted tube having its contents completely washed 

 out, and its basement membrane. left quite naked: this could happen 

 only as a consequence of a current of liquid passing through the tube, 

 and there is no known source of such a current but the Malpighian 

 vessels : the second proof is still more convincing and satisfactory, and it 

 is this y that a tube may often be seen entirely denuded of its epithelial 

 lining, and continuous with a Malpighian body, in the interior of which 

 the vessels are quite perfect. 



" Now, a tube of this kind deprived of its lining of normal epithelium 

 has manifestly lost its power of separating from the blood the solid con- 

 stituents of the urine, while, the Malpighian vessels remaining unaffected, 

 the power of secreting water remains. Further, it appears probable not 

 only that the Malpighian body continues to secrete water, but that the 

 whole length of a convoluted tube thus deprived of its proper epithelium, 

 and either remaining naked or lined by delicate nucleated cells, such as 

 those which cover the Malpighian vessels that the entire length of such 

 a tube becomes a secretor of water, which it abstracts from the portal 

 plexus of vessels on its exterior. This is rendered probable by the 

 appearance of the tube itself; and the probability is still further increased 

 by the fact of the tubes becoming, in some cases, dilated into cysts, which 

 usually contain a simple serous fluid, without any of the solid constituents 

 of the urine. 



" It has long been supposed that the simple cysts, which are so com- 

 monly seen in connection with some forms of renal disease, are, in fact, 

 dilatations of the urinary tubes. I am not aware that any satisfactory 

 evidence has been adduced in confirmation of this opinion, but there are 

 some facts and arguments which appear to me abundantly sufficient to 

 prove the accuracy of the notion. 



" 1st. The tubes thus denuded of their epithelium are often seen much 

 dilated. I have repeatedly seen them three or four times exceeding 

 their normal diameter. In some cases the dilatation is very sudden, so 

 that the tube assumes a globular form, and appears to bulge in the 

 intervals of the fibre-cellular tissue, in which the tubes are packed : in 

 some cases, too, the basement membrane appears thickened in proportion 

 to the dilatation of its cavity. Now, this process of dilatation having 

 once commenced, and the lower end of the tube becoming closed by a 

 deposit in its interior, or by pressure from without, there is no reason to 

 suppose that the process may not continue until a cyst as large as a pea 

 or a walnut is formed. 



" 2ndly. But there are other facts which afford a very interesting and 

 remarkable confirmation of this notion. In a case of simple acute or 

 chronic nephritis, the quantity of oil in the secreting cells of the kidney is 



