350 



which have no imbrication show it after maceration in distilled water. 

 This is evidently the result of mechanical forces. The fluid increasing 

 by osmosis causes pressure within the lumen against the cells. Under 

 pressure the fluid takes the direction of least resistance causing a 

 current in the direction toward which the cells are inclined. Bowman's 

 capsule is quite distended with fluid and vesicles. The epithelium of 

 the adjoining convoluted tubule is inclined toward the capsule. Tubular 

 epithelium is at times seen pushed within the capsular space. From 

 this evidence we conclude that there is a current from the convoluted 

 tubule into the capsule which causes the imbrication in the tubule near 

 its junction with the capsule. 



Brush-Border. 

 A normal kidney which shows no brush-border may be made to 

 show it by maceration in a hypertonic salt solution. The distilled 

 water specimens show no suggestion of brush-border, but all the salt 

 solutions from 0,9^'o to saturated solution bring it out in varying 

 degrees. The most favorable strength for its production is a 5<>/o 

 solution. In the 0,9% solution it is poorly developed and takes several 

 hours to appear. The stronger concentrations produce fair brush- 

 borders but not as high nor as clear as the 5% solution. The most 

 marked brush-borders are in the tubules lying near the medulla and 

 in the angle between two pyramids of Feurein. Here they may be 

 seen to consist of unquestionably definite, outstanding, independent 

 prolongations of the cell protoplasm. They are not supported by each 

 other nor by any substance between them. In the rest of the cortex 

 the picture is not so clear. Here it usually appears as a striated 

 border. The dark striations are generallv connected at their ends 



Fig. 4. Fig. 5. 



Fig. 4. Brush-border consisting of processes like cilia. From cortex macerated in 

 57o NaCl 3 hrs. X 780. 



Fig. 5. Brush-border appearing lilse striated membrane. From cortex macerated 

 in 27o*'/o NaCl 3 hrs. There is a basal granule at the bottom of each striation. The 

 interspaces are continuous with the cell protoplasm and are enclosed at their upper ends 

 ■where the sections show a membrane connecting each two adjacent striations. X 780. 



