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MANUAL OF HISTOLOGY. 



tour; in those of intermediate size it is thin, and has but a 

 single contour ; the largest tubes possess no basement-mem- 

 brane whatever. In the latter the great cylindrical cells are 

 held together by the prolongations above mentioned and a 

 colloid substance. The diameter of the largest tubules at the 

 apices of the pyramids is 0.2 to 0.3 mm., after the first division 

 0.1 to 0.2 mm., the smallest being about 0.06 

 mm. The height of the epithelium in the 

 largest tubules is between 0.02 and 0.04 mm. ; 

 in those at the boundary layer about 0.015 

 mm. Good specimens are obtained by im- 

 mersing a fresh gland in dilute muriatic or 

 nitric acid for a variable period (six to twenty- 

 four hours), and examining in dilute gly- 

 cerine. The collecting tubules' should be 

 injected from the ureter with blue or red gel- 

 atine, and the whole organ immersed in alco- 

 hol, until ready for cutting. Sections made 

 parallel to the collecting tubules produce 

 splendid specimens. The connection between 

 the collecting and convoluted tubules of the 

 human kidney cannot be shown by injection, 

 for the colored fluid thrown in from the ure- 

 ter rarely reaches the convoluted tubules of the first order. In 

 the lower animals fishes, frogs, etc. however, if the ureter be 

 injected under constant pressure the entire length of the urin- 

 iferous tubules may be filled with the carmine, or, better, Berlin 

 blue 2 fluid. 



Fio. 98. Kidney of 

 dog. Small collecting tu- 

 bule above the boundary 

 layer, x 450. 



1 In the pig Henle finds that two large collecting tubules begin at the apex of 

 each pyramid, then run along the outer borders of the cortical substance proper, 

 high up into the cortex, and there unite by forming a loop. Henle states that 

 the convoluted tubules empty into these, or their divisions by intercalated portions, 

 which he calls communicating tubules ( Verbindunffscanalchen). Eingeweidel. , p. 24. 



* This has been done by Frey with fishes and amphibia; by Hiifner with birds, 

 fishes, etc. ; by Gross with fishes and tritons, and by Hyrtl with some sorts of fishes. 

 According to Seraphina Schachowa (Unters. ueber die Niere. Diss. Bern. 18?(i) the 

 convoluted tubule of the first order is connected to Henle's loop by a spiral tubule, 

 while the ascending portion of the loop exhibits an expanded part immediately above 

 the loop, and a spiral part, which latter becomes continuous with the ascending limb 

 of the loop. Between the ascending part of the loop and the intercalated portion 

 Scbachowa describes a new tubule, which she calls the "irregular tubule." 



The spiral tubule is lined with an epithelium which has a striated appearance in 



