THE KIDNEY. 209 



tine l for the common oil. The renal artery or vein may also 

 be injected with absolute alcohol, and sections prepared as 

 above. But the epithelium suffers in this way, for the alcohol 

 causes the rods to shrink, and the colloid substance between 

 the rods coagulates. Still, the striated appearance is seen near 

 the membrana propria. Another fact which seems to have es- 

 caped Heidenhain is that alcohol so injected causes the nuclei 

 of the cells to recede toward the membrana propria by its 

 action on the rods. 



The action of water on the rods is peculiar. A fresh kidney 

 must be used and a portion of the cortical substance placed on 

 a slide, together with a drop of water ; it is then to be teased 

 with needles and immediately examined. At- first the rods are 

 not distinctly brought into view, but they soon appear with 

 their contours sharply delineated. This appearance, however, 

 does not last very long, for the epithelium soon imbibes water, 

 swells, and then forms an indistinct mass. 



In the neck of the convoluted tubules of the frog, coluber, 

 etc., the epithelium is ciliated. In the frog the cilia have great 

 length, but the convoluted tubules do not have the rod epithe- 

 lium. In the dog, cat, rabbit, etc., the rod epithelium begins 

 at the neck of the tubule and is continued as far as the loops. 



The convoluted tubules of the first order, after ramifying 

 in the cortical substance, become continuous with the looped 

 tubules of Henle, as already described. 2 The change takes 

 place in the vicinity of the boundary layer. 



The looped tubules. The looped tubules traverse the 

 medulla for a greater or lesser distance. A few almost reach 

 the apices of the pyramids ; others extend but a short distance 

 below the boundary layer, while a third class occupies an inter- 

 mediate position. Good specimens are obtained by macerating 

 vertical sections of the medulla in a solution of caustic potassa 

 (i to 1 per cent.). The potassa destroys the epithelium, the 

 stroma, and the blood-corpuscles, but leaves the basement- 



1 Resinous turpentine is prepared as follows : some common oil of turpentine is 

 poured upon a deep plate, so as to form a thin layer, and a piece of fine muslin is 

 snugly fastened over it to keep out the dust. The liquid is now exposed to the ac- 

 tion of the air. In a few days, if the weather be warm, or a week or more, if the 

 weather be cold, the turpentine will have become thick, yellow, and resinous, and is 

 now no longer transparent. Resinous turpentine, prepared in this way, forms one of 

 the best preserving agents. Its use will be spoken of further on. 



- Henle: Eingeweidel., 2te Aufl., p. 316. 



