118 A CYTOLOGICAL STUDY OF THE KIDNEY CELL 



impressed with the want of constancy in the appearance of the mitochon- 

 dria in different or even in the same microscopic sections from the same 

 kidney. This holds good also in the other groups. Serial sections prove 

 that in every kidney distinct variations in the structural picture of the 

 mitochondria of the same proximal convoluted tubule are always present ; 

 that is to say, the variations depend upon the level at which the section 

 is cut. There is always a gradual transition in the shape of the mito- 

 chondrial structure from one segment of the tubule to the other. Even 

 within the central limit of the segments studied such variations are pres- 

 ent. Then again neighboring segments of the same type but of different 

 tubular units may vary distinctly in the structural arrangement of their 

 mitochondria as to size, number, and shape. But such variations cannot 

 be the result of urea feeding, since they are also found in the kidneys 

 of the rats that were not fed any urea at all. There are about as many 

 variations as there are kidneys studied, and I am afraid one could carry 

 the descriptions of the various combinations of these on to the infinite. 

 True enough, on a general quick survey of the sections of the group 

 that received no urea, the picture of the kidney of the white rat described 

 for the normal, holds good, but when it comes to comparing even neigh- 

 boring sections of the same tubular group, variations are also found here 

 at once. For instance, there is a distinct difference in the granular disso- 

 lution in Figs. 8 and 12, which are sections from the controls of the first 

 group. But the same is true of the kidneys of the rats fed urea over a 

 long period (see Figs. 6, 9, 10). Then again the dogmatic picture which 

 has been described for the normal is represented by Fig. 11, but it is a 

 picture of the proximal convoluted tubule from a kidney exposed to a long 

 urea strain. Here the beautiful "batonne" arrangement is very apparent 

 and dominates the optical impression received. These instances merely 

 illustrate the point raised. 



In comparing the individual mitochondrial granules of the various 

 groups no hypertrophy was observed in those where urea had been fed, 

 and when compared to controls from the first and second group no nu- 

 merical increase could be established. It is impossible to segregate the 

 various groups of rats by the appearance of their mitochondrial apparatus. 

 Granular dissolution or breaking up of the solid rods is not any more a 

 characteristic of the urea kidneys than of the control kidneys (compare 

 Figs. 6 and 7, 9 and 12). Nor is the size of the granules produced dur- 

 ing dissolution any indication that the mitochondrial apparatus of the 

 proximal convoluted tubules is in any way affected by increased urea 

 secretion, since the same picture is found in controls that did not receive 

 any urea whatsoever. If we pay attention to the qualitative difference in 

 staining 1 it can be stated that there is none except for the usual normal 

 variation. 



