THE KIDNEYS. 233 



tubules, differs somewhat in appearance in the human 

 kidney as compared with that of the lower animals, 

 a portion of a perfectly healthy organ should be pro- 

 cured from the post-mortem room as fresh as possible, 

 and prepared for observation in the same manner. 



Preparation 7. The injected kidney. The 

 bloodvessels of the kidney will very probably be 

 filled in injecting an animal entire ; but, if this 

 should not have been the case, it is not difficult to 

 make a special injection of the separated organ from 

 the renal artery. The red gelatine injection may be 

 used, and the kidney is kept -warm, and the injection 

 maintained for a considerable time, in order that the 

 vessels of the glomeruli and the network of capilla- 

 ries in the cortical substance supplied by their effer- 

 ent vessels may be completely tilled. The organ is 

 then set aside in a cool place (surrounded by ice, if 

 possible), and, when the gelatine is completely set, 

 is cut into three or four pieces and hardened gradu- 

 ally, as usual, with alcohol. The sections, which 

 need not be very thin, but should be quite even, and 

 comprise the whole thickness of the organ, are to be 

 mounted, unstained, in dammar varnish. 



Preparation 8. Uriniferous tubules The uri- 

 mferous tubules may be injected from the ureters for a 

 considerable part of their length simultaneously, if it be 

 desired, with the injection of the bloodvessels by a solu- 

 tion of Berlin blue. But even if well filled they are too 

 densely arranged to render it possible to trace individual 

 tubules along their whole extent. This may be better 

 accomplished by making teased preparations of the kid- 

 neys of small animals, which have undergone some pro- 

 cess of preparation, having Cor its object the solution or 

 softening of the intertubular substance. Several such 

 processes have been proposed, but none yield entirely 

 satisfactory results. The best, perhaps, that has yet been 

 tried consists in digesting tolerably thick slices of a small 

 kidney in a mixture of four parts of spirit and one of 

 hydrochloric acid, kept boiling fur three or four hours. 

 The boiling is performed in a flask fitted with a cork, 

 through which M louo- vertical tube passes; in this much 



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