1906.] " KENAL-PORTAL SYSTEM." 889 



exci'etion takes place, the organ through which the blood-vessels 

 pass is the active agent*. Surel}^ such a reversal of activities 

 cannot be ignored ! And, confirmatory of this distinction between 

 the hepatic capillaries and most of those so-called of the kidney, 

 Hyrtl (2) t points out in the case of the " renal-portal system " 

 of the Frog that the venous connections betAveen the post-renal 

 veins on the dorsal surface, and the renal veins on the ventral 

 surface of the kidney, are so large that they can scarcely be called 

 capillaries. If we assume, as we logically must, that a given 

 function will, under similar conditions, always be performed in 

 the same manner, then, on this present account alone, the obvious 

 inference is that the "sinus-like system" forming the connection 

 between the postei-ior cardinal and postrenal veins has nothing 

 whatevei- to do with the elimination of excretoiy matter from the 

 blood, and this conclusion harmonises with the arguments already 

 advanced. 



Another objection may be urged. In the case of the hepatic- 

 portal system, e. (/., it is significant that there does not exist a 

 single instance throughout the vertebrate series of a by-path b}' 

 which the blood flowing forwards in the portal vein can evade 

 the passage through the livei' substance ; and it is evident that 

 this persistence in one course is explicable solely on the supposition 

 that it thereby serves an important physiological purpose, namely, 

 the elimination of food- products from the blood ; in other words 



* Dv. Arthur Keith has kindly called my attention to a paper on " The Question 

 of Sinusoids," by F. T. Lewis (Anat. Anzeig. August, 1904) in which the assertion 

 of this radical difference of origin of the respective vascular supplies of the liver and 

 " portal " kidney is denied. Not having investigated the subject myself I cannot 

 give a definite opinion (though, apart from other reasons, I cannot fail to be biassed 

 in favour of Shore, -whose paper is as lucid as that of Lewis is obscure), but will 

 content myself with the following suggestions. The " portal " kidney, which alone 

 has a sinusoidal blood-supply, owes this peculiarity, as I have shown in detail below, 

 solely to the facts that it is always well developed and therefore of considerable bulk, 

 and that it originates in the neighbourhood of a vein, on the lumen of which it encroaches 

 as growth proceeds. In the Common Herring e. g., only that portion of the left 

 kidney which, rising dorsally from the posterior limit of the body-cavity, comes into 

 contact with the left posterior cardinal, forms a small renal cardinal meshwork ; in 

 other words, there is no " renal-portal system " in the posterior part of the kidney. 

 No renal cardinal meshwork at all exists in connection with the right kidney which 

 does not coincide in position with the more medianly situated right posterior 

 cardinal. This individual instance well illi^strates the fact that the sinusoidal circu- 

 lation of the kidney, when it occurs, is solely due to contact with a vein. Compare 

 now the case of the liver, according to Lewis. Here there is no restriction of the 

 sinusoidal circulation to the region of contact between liver and vein ; on the contrarj', 

 the venous circulation iinds its way to eveiy part of the massive organ-^the blood is 

 the active element. I have also on p. 891 indicated another difference, histological 

 in character, between the vascular supplies of the' liver and " portal " kidney. 



But even assuming that Lewis is right in his statement that the vascular supplies 

 of the liver and " portal " kidnej' originate in the same waj', it does not in the least 

 affect the validitj'' of my theory as to the raison d'etre of the " renal-portal system," 

 since he also states that the vascular supply of the myocardium is sinusoidal, and 

 this is certainly not developed in connection with an excretory or portal function, and 

 what is true of the myocardium aiay be true of the kidnej'. 



Dr. Shore writes to me, in reference to Lewis's paper, that " he does not see any 

 reason to alter the opinion he had previously arrived at. The development of the 

 venous sinuses in the li\'er is certainly that of a penetration of blood-tubes into the 

 hypoblast mass." 



t See also footnote on p. 891. 



59* 



