A- New Conception of the Glomerular Function. 573 



with the blood-pressure, as should be the case were filtration the essential 

 factor in determining the volume of the urine discharged from the kidney. 



In the third place we have very decisive evidence against the Ludwig 

 theory in experiments designed to test the second assumption in that theory, 

 namely that of reabsorption. If this is a process which occurs extensively 

 within the tubules, and we bring into play any factor which favours 

 reabsorption, we ought to effect a diminution in the volume of 

 urine yielded by the kidney. Such a factor is an increase in hydro- 

 static pressure within the ureter, tending to prevent the outflow of 

 urine. All that is necessary is to make the kidney discharge against a 

 small pressure. The experiments carried out by most experimenters 

 upon these lines have indeed yielded results which may be interpreted as 

 indicating increased reabsorption. But we may urge as a general criticism 

 against such results that the degree of decrease of urine flow is surprisingly 

 small when we remember how essential it is according to Ludwig's theory to 

 assume that reabsorption is excessively free. The kidney working against 

 even a small hydrostatic pressure ought to show far greater reabsorption than 

 was actually obtained. But the whole idea of reabsorption as an active pro- 

 cess in the formation of urine has been completely disproved by Miss Cullis 

 and myself,* for we were able to prove that decrease in rate of the urine 

 flow when a kidney was made to secrete against a pressure was only a 

 universal result when the animal was under an anaesthetic, and that if the 

 animal were pithed and the experiment then performed in the absence of 

 an anesthetic, the kidney working against a small pressure always excreted 

 more salt and usually more water than the opposite kidney .f The action of a 

 pressure then tends to excite the kidney to greater activity, a result which 

 entirely disproves the possibility of reabsorption being an extensive factor 

 in the normal formation of urine. 



Yet another point which militates greatly against the idea that the 

 glomerulus is a filter is the behaviour of the kidney after temporary 

 asphyxiation. If the renal artery be clamped for one minute and then 

 released, the kidney does not at once begin to secrete, although the blood 

 flow returns at once. It is only after a variable, but usually considerable 

 delay that the kidney restarts, and at first the urine flow is very slow, 

 only gradually returning to a rate comparable to the initial flow. If the 

 artery has been clamped for any length of time the urine first collected after 



* Brodie and Cullis, ' Journ. of Physiol.,' 1906, vol. 34, p. 224. 



t Subsequent to these experiments I have found that, under the same conditions, the 

 blood flow through the kidney is not altered by the small rise in ureter pressure employed 

 in our experiments. 



2x2 



