UEINE. 



221 



A great part of the water, 

 Fig. 130. 



thelial cells of the uriniferous tubes, 

 however, is doubtless 

 obtained by mere trans- 

 udation into the urini- 

 ferous tubes from the 

 vessels which form the 

 Malpighian tufts or bo- 

 dies. Hence increased 

 pressure of blood in the 

 finer renal vessels causes 

 increased separation of 

 water and of the solids, 

 especially the salts. If, 

 on the other hand, the 

 arterial and capillary 

 tension is diminished, 

 the secretion is also di- 

 minished. It, however, 

 by no means follows, as 

 Lehmann implies, that 

 the secretion of urine is 

 a mere physical pheno- 

 menon, dependent upon 

 the fact that the blood 

 undergoes compression 

 while in the vessels of 

 the Malpighian tufts. 

 The more characteristic 

 elements of the urine 

 are separated by a vital 

 action of the epithelial 

 cells, and hence their 

 amount in twenty-four 

 hours is more nearly 

 constant in health; while 

 a great part of the water, 

 and of the salts proba- 



blv when in P^PPQQ in Structure of the kidney. 1. Coecal extremity of a tubulus 



Diy, W eXCeSS in nriniferus . 2| 2 . Recurrent loops of tubuli. 3, 3. Bifurcation 



the blood, are Separated of tubuli. 4, 5, 6. Tubuli converging towards the papilla. 7,7, 



from tVlP lattpr hv tranc 7 ' 7 ' Corpora M alpighiana seen to consist of plexuses of blood- 



Om tne latter by trans- Vesse l 8) connected with a capillary network. 8. Arterial trunk. 



