114 A CYTOLOGICAL STUDY OF THE KIDNEY CELL 



derived from mitochondria las pointed out by Ophiils(17), but if that is 

 so it is evident that some change has occurred involving radical altera- 

 tion in the staining affinity of the mitochondrial substance. 



Results of Fixed Tissue Studies 



In studying the low-power picture the cortex stands out massively 

 on account of the mitochondrial richness of its tubules. This picture 

 varies in its color intensity with the variations in mitochondrial density 

 and also with the variations in fixing agents. Nevertheless, the color 

 coefficient between medulla and cortex remains stationary. On viewing 

 the cortex, even with the lowest power, one -can easily distinguish the 

 proximal convoluted tubules on account of their greater staining intensity. 

 Fig. 1 gives a fair demonstration of the difference in color density between 

 proximal and other tubules of the cortex. 



In comparing sections from the four groups of kidneys differences 

 could always be found, but further study invariably showed that such 

 differences also existed within the individual group and therefore could 

 not be used in differentiating the groups. Only the study of serial sections 

 can protect against unwarranted conclusions. As a demonstration I wish 

 to cite an observation which, without serial study, would easily have led 

 to faulty inferences, if coincidence should have thrown the observations 

 mostly into one group of tissues. 



In the studies of the group described by Dr. Addis a peculiar picture 

 of divisional action of groups of convoluted tubules is observed, if one 

 may use this term for the sake of simplicity (see Figs. 2 and 3). It is 

 at once apparent that in some tissues entire groups of convoluted tubules 

 with their connecting segments (Schaltstiicke) stand out very plainly by 

 virtue of their mitochondrial concentration in contrast to other neighbor- 

 ing groups, which have less and fainter staining, but otherwise similar 

 appearing mitochondria. A casual observer might be easily misled by 

 such a picture. In this study it seemed at first that such a grouping was 

 more often seen in the tissues of the rats which had undergone prolonged 

 urea feeding. But the study of a large number of sections from all the 

 groups dissipated this impression. All kidneys showed this peculiarity in 

 some part or other of their structure. While this phenomenon does not 

 give any help in differentiating the kidneys of urea- fed from control rats, 

 it is of interest in relation to Lindemann's(32) hypothesis of a division 

 of labor in the individual kidney in which certain groups of tubules sup- 

 posedly are allowed to rest while others are active. At any rate it illus- 

 trates the fallacies of drawing conclusions from sections which are not 

 representative of the entire organ. 



The absence of any appreciable increase in the weight of the kidneys 

 in Group I, which had been fed urea over a long period, precluded the 

 existence of any gross difference in the number and size of the cells as 



