115 



from the renal arteries into the ureters, or excretory ducts of the kid- 

 neys ; a convincing proof of immediate communication among theminute 

 arteries, which exceedingly tortuous form, with the minute veins, the 

 cortical or outward substance of the kidneys, and the straight urinaey 

 tubes, which distributed in conical fasiculi, in the interior of these or- 

 gans, constitute what has been called its tubuli and papillae. The passage 

 of injections from the arteries into the renal veins, is as easy ; and I have 

 often seen the coarsest liquids flowing at once by the ureters and by the 

 emulgent veins. This free communication between the arteries, the 

 veins, and excretory ducts of the kidneys, gives an idea of the ra- 

 pidity with which the blood must flow through these organs, whose 

 firm consistence allows a very moderate dilatation io the vessels ; and 

 suggests the possibility of a sort of filtration of the urinary fluid, the se- 

 cretion of which would be only succession of chemical or mechanical se- 

 parations, from the blood, in its passage along very minute ducts, of a 

 bore progressively decreasing. This was the opinion, at least, of Ruysch, 

 whose system on the intimate composition of our organs, and on the im- 

 mediate continuation of the blood-vessels with the excretory ducts is 

 chiefly founded on the facts of structure, discovered to him by his beauti- 

 ful injections of the renal arteries. 



The kidneys are of duller sensibility, and less energetic action than the 

 other glands. The force of life has less to do in their secretion, and their 

 functions may be more readily explained on the principles of chemistry 

 or hydraulics. 



XXXIII. If we attempt, indeed, to apply to the urinary organs the 

 fundamental laws on the mechanism of secretions*, it is not seen, that 

 these organs are not under their absolute controul. Of all the animal 

 fluids, urine is the one most complex in its elements, and most variable in 

 its qualities. Not only do foreign substances- sometimes appear in it, af- 

 feet, and even change its composition; other fluids may, at times* J*ix 

 with it, and disguise it altogether. Thus credible observers tells us 

 appearance of urine, of bile, fat, milk, blood, pus* of which m^ v 

 may be found collected in Mailer's great work on physiology, The kid- 

 neys, then, have less sensibility than the other secretory organs : they 

 reason less, if I may venture on the expression, on these^ at ^ on P ro ^ uce d 

 by the various substances in the blood : their action^ also less power- 

 j Z. . 



fort on the Maine, says, that he has seen exactly this st^ ct . ure .. from injections of the 

 hepatic vein, and therefore he infers that the anatonv ot tne Ilver and kidney may be 

 similar in other respects. 



From these glandules, EYSENUARBT says' " t^ 1 tne g^yish and transparent urini- 

 ferous vessels, which seem to be articulated, *' lse - Tnese vessels form a net-work, 

 which every where unites the glandules witb~ ach other - He therefore thinks SCHUM- 

 I.ANSKT was deceived, in supposing that - ach glandule had a secretory duct, which, 

 after making numerous curves, ran strait into the medullary substance. 



" Little precise information is give* b 7 EITSENHABDT respecting the medullary part. 

 The excretory ducts, however, whir 1 "become straight when they pass out of the corti- 

 cal substance, pass along in fascic^ 1 f about twenty in each fasciculus. 



" In a foetus, the cortical substance was smaller in proportion, and the glandules were 

 of scarcely half the size. Eac* vascular vessel of the medullary substance was com- 

 posed of granulations ; somef them being voluminous, and others much smaller, and 

 all strongly pressed against each other, so that the vessels could no longer be distin- 

 guished from each other, but their passage only marked by striae. The granules were 

 not produced by putrefaction, although putrefaction gives a globular appearance to 

 these parts." Copland. 



* See the Chapter on Secretion* 



