ADEQUACY OF BLOOD PRESSURE 715 



filter fluid. We are therefore driven to think that the anuria is 

 due to some change in the vital properties of the membrane. 

 And, if it is once admitted that the living cells can resist success- 

 fully all filtration through them, it certainly seems likely that 

 they must under normal conditions have the power of regu- 

 lating independently of the filtering force the material which 

 passes through them. 



On the whole, the little knowledge we have of the properties 

 of Bowman's membrane is in favour of Heidenhain's view. But 

 as it is impossible to come to a definite conclusion, we may still 

 inquire whether, granting the properties to this membrane neces- 

 sary to Ludwig's view, the filtering force is sufficient to produce 

 filtration under all the conditions in which urine is formed. 



Adequacy of Blood Pressure as the Filtering Forced- 

 According to Ludwig's view the only force available for filtration 

 in the glomerulus is that of the capillary blood pressure, a force 

 which we unfortunately have no means of measuring directly, but 

 which is certainly small. Consequently, no decrease in the con- 

 centration of crystalloids in the glomerular filtrate as compared 

 with the blood would be possible ; for any such decrease would 

 produce an osmotic resistance to filtration which the available 

 filtering force would be inadequate to overcome. 



Starling has attempted to obtain evidence in favour of 

 Ludwig's view by the following line of research. He determined 

 the osmotic pressure of the serum proteids, and from the value 

 so obtained calculated that the osmotic pressure of the plasma 

 proteids would correspond to about 40 mm. Hg. From this 

 it follows that when the filtering force falls to 40 mm. Hg 

 filtration must cease. And in accordance with this it has been 

 often found that, when the arterial blood pressure falls to about 

 this figure, the secretion of urine stops. Starling tried to prove 

 the same point in another way. According to Ludwig's view 

 ureter pressure is a derivative of blood pressure, and, when the 

 ureter is completely obstructed, will reach a height which is 

 equal to the capillary pressure minus the osmotic pressure of 

 the plasma proteid. From this it follows that the ureter pressure 

 will always remain about 40 mm. Hg below the blood pressure, 

 and that when it has reached this level the formation of urine 

 must cease. Starling injected diuretin into a dog and found 



1 See Editor's note, page 618. 



