EXPLANATION OF PLATES 123 



EXPLANATION OF PLATES 



Technical Remarks: All photographs were taken with a Zeiss micro- 

 scope on Cramer isochromatic plates. For illumination a 4-5 amp. Leitz 

 arc-light filtered with a single potassium bichromate (Orth) screen was 

 used. The ocular used for all pictures is No. 4, the objective for "low 

 power" is No. 3, for ''high power" No. 6, and for "oil-immersion" No. 

 1/12 apochromatic. The difference in size of corresponding structures in 

 different pictures photographed with the same microscopical magnification 

 is due to slight differences in the length of the bellows of the camera, 

 which has to be varied according to various circumstances. For printing 

 Azo "E and F hard" were used. 



All preparations reproduced here were fixed in either Regaud's or 

 Bensley's formalin bichromate mixtures, and stained with a modified 

 "Altmann anil in fuchsin," in which the destaining of the plasma with 

 picric acid had been carried over the usual point. This assures a high 

 contrast for mitochondria. Only Figure 2 is from a copper-chrome-hema- 

 toxylin preparation. 



Figure 1, low power, urea fed just before the death. The proximal 

 convoluted tubules stand out by virtue of the greater density of the mito- 

 chondrial content. This is the typical low power picture. 



Figure 2, low power, urea fed just before the death, and Figure 3, 

 low power, urea fed over a long period. In contradistinction to Figure 1, 

 Figures 2 and 3 show a distinct localized staining reaction of certain 

 tubular groups, while the neighboring and otherwise same structures re- 

 main faint in outline. In the left-hand corner of Figure 3 the usual pic- 

 ture is approached again. The localized staining reaction is due to the 

 greater mitochondrial concentration in this region and occurs in any 

 kidney under ordinary circumstances. Figure 3 is somewhat obscured 

 by faulty illumination. 



Figure 1, high power, urea fed just before death, and Figure 5, high 

 power, no urea fed, represent the usual dogmatic picture of the mito- 

 chondrial distribution in the kidney of the white rat under ordinary 

 circumstances. That one dose of urea has no influence on the mito- 

 chondrial apparatus is seen in Figure 4 by the unchanged appearance and 

 distribution of the granules. The proximal convoluted tubules stand out 

 very distinctly. The lumen is narrow. The brush border cannot be dis- 

 tinguished, for reasons explained elsewhere. The distal convoluted 

 tubules, connecting segments (Schaltstiick) and the limbs of Henle's loop 

 are distinguished easily. The descending limb of the latter is free from 

 mitochondria. The distal convoluted tubules (segment intermediaire, 

 Schweigger-Seidel's Zwischenstiick) are recognized by the wider lumen 



