THE KIDNEY. 215 



plished by the artery, under constant pressure (mercury). 

 Beale's blue injecting fluid l answers very well ; the writer's car- 

 mine-glycerine fluid 3 also acts exceedingly well, but it is very 

 difficult to obtain a good double injection of artery and vein. 

 I have found the most successful method to be the following : 

 Take a fresh bloodless kidney (dog, pig) and inject the vein 

 under constant pressure with the blue gelatine mass. 3 Next 

 place the kidney in iced water for a few minutes to harden the 

 gelatine, and then attach to the artery a very small constant- 

 pressure injecting apparatus, the receptacle for the injecting 

 fluid containing the writer' s carmine fluid. After regulating the 

 amount of pressure, the whole apparatus, with the kidney, is 

 placed within the receiver of an air-pump and the air slowly 

 exhausted. In this way the arteries become filled with fluid. 

 Allow the gland to harden in alcohol and mount the sections 

 in balsam or dammar. Kidneys in which the vein and artery 

 have been injected may have the collecting tubules filled from 

 the ureter with yellow injecting fluid, thus making a triple 

 injection. Sections of kidney hardened in alcohol may be 

 stained with borax- carmine, and afterward bleached in a di- 

 lute hydrochloric acid (1 to 10) solution, or a concentrated one 

 of oxalic acid. When the vessels of a kidney have been injected 

 with blue gelatine, staining with carmine gives good results. 



Thiersch's yellow injecting fluid is made as follows : Prepare a solution of 

 bichromate of potassa, one part of the salt to eleven parts of water, and a solu- 

 tion of nitrate of lead of the same strength. One part of the potassa solution 

 is placed in a small basin and mixed with four parts of a concentrated solution 

 of gelatine. Two parts of the lead solution are placed in another basin and 

 mixed with four parts of jelly. These are to be slowly and thoroughly mixed 

 together at a temperature of 75 to 90, and then heated in a water-bath at a 

 temperature of 212 for half an hour or more. Filter carefully through flannel 

 (Beale : Microscope, p. 90). 



The kidney stroma. In the cortical substance the stroma 

 is reduced to a colloid material which binds the tubules to- 

 gether. In the lower part of the medulla, in the fresh state, 



1 See page 205. 



* Carmine, 5 grammes; glycerine (anhydrous), 50 grammes; add caustic potassa 

 until the carmine is dissolved, and neutralize with pure, concentrated muriatic acid. 



3 Gelatine should be first immersed in water until it becomes softened and then 

 gently heated until dissolved. Add soluble Berlin blue, or Beale's blue fluid, until a 

 good color is obtained. Inject while hot. 



