365 



cretory parts of the tissue, appears to indicate a similar functional 

 relationship between the epithelium and the blood in the two organs^); 

 and justifies the inference that the renal portal circulation is excretory 

 in function. 



Physiological considerations. 



There is a good deal of evidence to be derived from a consider- 

 ation of the physiological aspects of this problem, although most of 

 the experiments were directed rather towards elucidating the roles 

 played by the various parts of the secretory apparatus, than to the 

 consideration of the question of the renal-portal system. 



These experiments commence with the work of Nussbaum (14) 

 who shewed that ligature of the renal arteries led to the cessation of 

 the flow of urine, which he explained as the result of cutting the 

 glomeruli out of action by depriving them of their blood supply. 

 Adami (1), whose ligature experiments gave a different result, due, as 

 Beddard (5) afterwards pointed out, to incomplete ligature, records 

 the following observation : "Experiments upon normal frogs shewed 

 that hsemoglobinurea could be most surely produced by introducing 

 laky blood into the venous system through the vena abdominalis an- 

 terior". In the paper already cited Beddard repeated and confirmed 

 the original experiments of NussbauxM and proved beyond all doubt 

 that arterial ligature produces absolute cessation in the flow of urine. 

 This at first sight appears to shew that secretion is entirely due to 

 the arterial blood, but at the same time it was pointed out that such 

 a deprivation of the oxygenated blood caused a rapid degeneration of 

 the kidney tubules. It was experimentally shewn by Barcroft and 

 Brodie (3 and 4) that a large amount of oxygen was required by the 

 kidney during the excretory activity. Bainbridge and Beddard (2) 

 taking the precaution, after ligature of the renal arteries, to keep the 

 frogs in an atmosphere of oxygen at ordinary pressure, were able to 

 obtain a secretion of urine by the sub-cutaneous injection of diuretics. 

 These diuretics were injected "either into the dorsal lymph sac, or 

 under the skin of the thigh" and so they must have been conveyed 

 to the kidney by one of the factors of the renal portal system. There ' 

 was here no increase of pressure in the kidney, as the arterial pressure 

 from the renal arteries had been removed, and only the venous pres- 

 sure left. It seems from these experiments that we are justified in 



1) lu the myocardium there is an absence of a secretory epithelium, 

 and so we have no such secretory activity manifested. 



