RESULTS OF FIXED TISSUE STUDIES 115 



compared with the second group. Yet, it was thought possible that there 

 might be a constant difference in the minute structural arrangement with- 

 in the cell, and a careful comparison was therefore made in order to de- 

 termine whether such qualitative distinctions might not be associated with 

 the various degrees in urea -feeding, especially as compared with the group 

 which did not receive any urea at all. 



In studying the general cell picture one finds that the height of the 

 cell of the proximal convoluted tubule is fairly constant, and such varia- 

 tions as exist seem to depend somewhat on the mitochrondial content of 

 the cell. If the content is low the '.cell cupola is high and the lumen is 

 very narrow (see Figs. 6 and 7). This is especially true when the mito- 

 chondrial apparatus is in a state of advanced granular dissolution (see 

 Fig. 8). With the increase in the numerical content of the mitochondria 

 the cell becomes somewhat lower. The cell cupola at once becomes clear 

 and the plasma just at the base becomes transparent. The more definitely 

 the mitochondrial apparatus assumes the "batonne" arrangement the 

 more apparent becomes this decrease in cellular height (see Fig. 11). 

 With this go certain variations in configuration and width of the lumen. 

 When the mitochondrial content is low and the plasma is dense through- 

 out the cell the lumen is narrowest and somewhat stellate in character 

 (see Figs. 6 and 7). As soon as the granular structures become definite 

 in their arrangement, the lumen widens and only fine strands of proto- 

 plasmic material bridge the lumen in an irregular fashion (see Fig. 12). 



In comparing the cells of the tubular structure of the kidneys of the 

 various groups it was at once apparent that those from animals fed urea 

 did not show any evidence of a distinctive increase in the size of the cells 

 of any part of the tubular apparatus. In any kidney from any group it 

 was possible to find the lesser degrees in variations in the size of individ- 

 ual cells which have been discussed above (see Figs. 9 and 10). One may 

 therefore conclude that urea feeding does not stimulate hypertrophy of 

 the cell of the kidney even if such feeding is carried to the extreme by 

 extending it over the life period of the animal in question. 



Also the appearance of the brush border does not offer any conclu- 

 sive evidence that it is influenced in any way by the forced feeding of 

 urea. I cannot agree with those writers who think that the variations 

 in the morphological appearance of the brush border are indicative of 

 phases in the secretory process. By some it is claimed that it gradually 

 rises, due to cellular pressure, until it is thrown off to allow the secretory 

 material to enter the lumen. Others do not share this view, and consider 

 the passage of secretion material as a true secretion phenomenon. Espe- 

 cially Sauer(33) in his earlier studies opposed the former idea, since he 

 always found a typically striated appearance of the brush border at any 

 stage of secretion. Of late Kolster(6) once more has drawn attention to 



