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Prof. T. G. Brodie. 



the re-establishment of the circulation contains protein, casts, even haemoglobin, 

 indicating considerable damage to the renal epithelium, either of the tubules 

 or of the glomeruli or of both. But even if the glomerular epithelium be 

 damaged it is inconceivable that this should temporarily abolish all the 

 filtering properties it formerly possessed, and it is just as difficult to under- 

 stand why the recovery of its power to filter should occur so gradually when 

 the asphyxiation is arrested. 



Let us next turn to the evidence that has been sought in favour of Ludwig's 

 theory from experiments upon the maximum ureter pressure. One of the 

 earliest attempts to associate the formation of urine directly with the blood- 

 pressure was a measurement of the maximum height to which the kidney 

 could force the urine up a vertical tube. As is well known, in the case of 

 the salivary gland, the gland can secrete water to a pressure exceeding that 

 of the blood in the carotid artery, a clear indication that a new force, 

 viz., one exerted by the salivary gland cells, is at play in producing the 

 result. But in the case of the kidney the result is very different. For the 

 maximum ureter pressure always lies below the aortic blood-pressure, and 

 usually some 30-40 mm. Hg below that pressure. The results were therefore 

 interpreted by supporters of the filtration theory as indicating that as soon 

 as the pressure within Bowman's capsule reached a point some 30 mm. Hg 

 below the glomerular blood-pressure, filtration ceased, and Starling* explained 

 the difference between the aortic pressure and the maximum ureter pressure 

 as being the pressure difference necessary for the separation of the blood 

 proteins from plasma, for he estimated the osmotic pressure of the blood 

 protein at that amount. It has since been shown, however, that the protein 

 osmotic pressure is certainly much less than this. Moreover Starling failed 

 to allow for a loss of pressure between the aorta and the glomerular 

 capillaries. Without doubt the loss of pressure between these points is less 

 than in the case of ordinary capillaries, for the resistance in the kidney arterioles 

 when dilated is certainly much less than at most points on the systemic 

 circulation. As I shall show later, the maximum ureter pressure as ordinarily 

 taken is a measure of the blood-pressure in the glomerular capillaries. 



But a still more difficult problem is offered to those accepting the filtration 

 theory in explaining these experiments. As was first pointed out by 

 Heidenhain,f upon the Ludwig theory the maximum ureter pressure should 

 be that pressure which just suffices to effect complete reabsorption of all the 

 glomerular filtrate. Upon the theory we are to imagine an absorbing surface, 

 capable of absorbing water, chlorides, urea and most of the bodies filtered in 



* Starling, ' Journ. of Physiol.,' 1899, vol. 24, p. 317. 

 t Heidenhahi, ' Hermann's Hdb.,' vol. 5, p. 327. 



