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MANUAL OF HISTOLOGY. 



mine through the kidneys. If a larger quantity of indigo 

 solution be injected, and the animal dealt with as above, the 

 second stage of the excretion is seen. Here, again, the glome- 

 ruli, the capsules, and the collecting-tubules are free from 

 color, the rod-epithelium stained blue, and their nuclei dark 

 blue (Fig. 101, F). In a few of the convoluted tubules and the 

 ascending broad branches of the loop, crystals of indigo-salt 



PIG. 101. Kidney of dog. Natural injection of secreting portion, artificial injection of artery, vein, 

 and capillaries. Transverse section through cortical substance : A, afferent vessel, filled with injected 

 material ; B, efferent vessel, also filled with injection ; B, glomernlus, injected and lying within its cap- 

 sule: epithelium of latter distinctly seen : D, capillaries surrounding the convoluted tubules, and dis- 

 tended with the injection ; at this point four capillaries are seen to unite and form a vein ; C, convo- 

 luted tubule, filled with crystals of indigo-carmine ; F, convoluted tubule, in which the nuclei have a 

 dark color. The striations of Heidenhain are beautifully shown in the convoluted tubules, x 200. 



fill the lumina. So, also, in some of the descending narrow 

 branches of the loop. In the third stage the rods are color- 

 less, while their nuclei are still blue. Masses of the indigo- 

 salt fill the lumina of the convoluted, looped, and collecting 

 tubules ; the glomeruli and their capsules are colorless. In 

 the last stage, the salt is contained in the lumina of the col- 

 lecting tubules only, all the rest of the gland being free from 

 it, and consequently colorless. From the above it will be 



