URETER PRESSURE. 183 



and 45 "/ as may be seen in the protocol given above. The difference in 

 the rate of urinary flow is undoubtedly due to a decreased flow of blood 

 through the kidney. 



But further than this somewhat unimportant difference in the rate 

 of rise of the ureter-pressure to its maximum is the lessening of the 

 minimum difference between blood and ureter-pressure which the more 

 rapid flow produces. As Heidenhain quite correctly pointed out, the 

 ureter-pressure represents not a secretion pressure but the pressure at 

 which secretion (or filtration) and reabsorption balance each other. The 

 theoretical maximum ureter-pressure, or minimal difference between that 

 and the blood-pressure, required to show the existence of a filtration 

 pressure which is needed to overcome the proteid osmotic pressure 

 of Starling, can only be obtained when the rate of Absorption is 

 negligible when compared with the rate of urine production. That the 

 point of balance is not reached by a slowing of the production process 

 (absorption not being admitted to occur) seems to be pretty well esta- 

 blished by the studies of Cushny on the salt distribution in urine of 

 two kidneys, one secreting against pressure, and the similar experiments 

 of Rudel on the urinary reaction. Fresh evidence, also, in favour of an 

 absorption occurring will be offered in this paper. It is to be noted that 

 Fig. 6 B represents a minimum difference of 64 mm., rate of outflow 

 13 drops per min. ; A a difference of 73 mm., rate of flow 2. That in my 

 experiments I did not more closely approach Starling's minimum 

 difference is probably due to the experiments having been performed in 

 hot weather when the animals were poor in water and consequently 

 unable to react to diuretics with an abundant secretion. My experi- 

 mentation has led me to feel strongly that many confusions and diffi- 

 culties in previous studies of the kidney secretion are largely due to 

 overlooking the important factors of the water content and of the salt 

 content of the animal as a whole. A subsequent paper will be devoted 

 to their study. That a certain rapidity of flow is necessary to produce 

 the minimum difference between blood-pressure and ureter-pressure 

 with any given constitution of the plasma suggests that absorption occurs 

 as a normal act and that the minimum difference is but the product of 

 these two factors balancing against each other. 



The need of a better demonstration of the possibility of reabsorption 

 from the tubules led to a further series of experiments. Other observers 

 have been more or less successful in injecting the tubules from the 

 ureter, but as a review of their methods and results is contained in a 

 recent paper by Lindemann it seems unnecessary to discuss them. 



