ELECTRON MICKOSCOPY' 





N 



^^•-P 





^ 







'i« 



■'.*• 







10 



-P 



'gi '■ • ^' % - ■ /^ '■ 



^♦•'.r 



^ -w 



- ^ ' 



» « 







^ f 





v>'^j 





t^^^c 



^'l^f *^ 





>'»^^ 





L^--" 



,d^ ^mI *-T-^iii«* 







Fig. 3. Cross section of a mouse kidney proximal convolution (top) and a distal convolution (bot- 

 tom) with surrounding capillaries (C). In both tubules the nuclei (N) and mitochondria (M) are evi- 

 dent. The lumen is usually closed in the proximal convolution but open (Lu) in the distal. Numerous 

 brush border extensions (B) line the cells in the proximal convolution but only few microvilli (Vi) in 

 the distal convolution. Vacuoles (V) containing autofluorescent material are prominent. Occasionally, 

 a cilium (Ci) is encountered in the distal convolution. Magnification 2,900X. 



cupying the space that normally would be mal convolution and the abundance of brush 



called the lumen of the tubule. Evidence is at border extensions seems to facilitate this ac- 



hand showing that about 85 per cent of the tivity of the cells by largely increasing their 



urine reabsorption takes place in the proxi- absorptive surfaces. Therefore, the w'ay the 



168 



