THE KIDNEY. 211 



this portion of the loop is greater than in the convoluted tu- 

 bules. Specimens prepared with the neutral chromate of am- 

 monia, as before detailed, give good results. Vertical sections 

 may be made from a kidney macerated in the ammonia solu- 

 tion and afterward treated with alcohol ; or, better, from frozen 

 specimens. 



The broader extremity of the looped tubule ascends through 

 the medulla into the cortical substance and becomes continu- 

 ous with a convoluted tubule of the second order (Fig. 91, i). 

 These tubules, the intercalated portions, 1 greatly resemble con- 

 voluted tubules of the first order, as already mentioned. Spe- 

 cimens should be prepared in the same way as those of the 

 latter. The convoluted tubules of the second order, after rami- 

 fying in the cortical substance, terminate by emptying into the 

 collecting tubules (Fig. 91, J). 



The collecting tubules and their epithelium. The collecting 

 tubules a possess cylindrical epithelia, the bases of which are 

 irregular and present point-like prolongations 3 (Fig. 97), which 

 interdigitate with one another. The nuclei in 

 the smaller collecting tubules are large and 

 very prominent, but the protoplasm which sur- 

 rounds them is not very abundant. The base- 

 ment membrane is comparatively thick and 

 exhibits a double contour. The smaller col- 

 lecting tubules are situated in the cortical sub- 

 stance, a little distance below the capsule. 



_,. _ FIG. 97. Kidney of 



Their diameter ranges between 0.04 and 0.06 d s- isolated ceiis of 



two collecting tubnles, 



mm. The small tubules unite to form larger Bowing irregular base 



and point-like prolonga- 



ones, and these again to form tubules of still jJJSiiS 



larger diameter. The irregular appearance at from one^near boundary 

 the bases of the epithelia is the same in the 

 larger trunks as in the smaller branches ; in the former, how- 

 ever, the cells are larger, and the protoplasm more voluminous 

 than in the latter. The nuclei have about the same size in 

 each (Fig. 98). The basement-membrane diminishes in impor- 

 tance in an inverse ratio with the size of the collecting tubules. 

 In the smaller ones it is prominent and possesses a double con- 



1 Schweigger-Seidel : Schaltstiicke ; Roth : Verbindungscanale (connecting tu- 

 bules). 



2 Open tubules of Henle. Zur Anat. der Niere. Gottingen, 1862. 



3 Heidenhain : loc. cit. 



