THE URINARY TRACT. 739 



the capillaries of the collecting tubules and from the vasa recta, 

 the ascending loops of which empty directly into the inter-zonal 

 venous plexus. 



According to C. Ludwig, the capillaries of the capsule and of 

 the surrounding fat-tissue of the kidney, which arise partly from 

 small "branches of the renal artery before it reaches the bounding 

 zone, are united directly to the capillaries of the kidney-tissue. 



The uriniferous tubules originate from the capsules of the 

 tufts, opposite the site of the blood-vessels, as first discovered by 

 Bowman, and terminate, after uniting and being considerably 

 reduced in numbers, at the papilla of the pyramid. They are 

 chiefly of two kinds : convoluted and straight. The former con- 

 sist of convoluted tubes of the first and second order ; the latter 

 are the straight, narrow and straight, collecting tubules. The 

 convoluted tubules of the first order occupy the portion around 

 the ascending branches of the renal artery, and their sum total 

 is termed the " labyrinth " by C. Ludwig ; the convoluted tubules 

 of the second order fill the most external portion of the cortex, 

 in which there are no tufts. The straight tubules, both narrow 

 and collecting, produce the medullary rays between the laby- 

 rinths in the cortex while in the pyramids they run in separate 

 bundles according to the following arrangement : First, the nar- 

 row tubules, together with the vasa recta, in the imaginary pro- 

 longations of the labyrinth, and then the collecting tubules as 

 direct prolongations of the medullary rays of the cortex. Fig. 

 333 represents the generally adopted schema of the course of the 

 uriniferous tubules, first issued by Ludwig and Schweigger- 

 Seidel. The results were, obtained both by isolation of the urin- 

 iferous tubules, by means of maceration in dilute acids, and by 

 the study of kidneys in which the blood-vessels and uriniferous 

 tubules had been injected with colored gelatine. In this depart- 

 ment C. Ludwig was most successful. (See Fig. 333.) 



The details are as follows : The convoluted tubule (of the first 

 order) originates from the capsule of the tuft as a slightly nar- 

 rowed, funnel-shaped neck, and, after repeated convolutions 

 within the labyrinth, tends toward the medullary ray. Here it 

 becomes (to varying depths) narrow, often exhibiting spiral 

 windings (Schachowa) before decreasing in caliber, and repre- 

 sents the descending branch of the loop, or Henle's tubule. This 

 enters the pyramidal substance, producing a distinct, angular 

 divergence at the dividing zone between cortex and pyramid, in 

 order to reach the bundles of the vasa recta. After reaching 



