120 A CYTOLOGICAL STUDY OF THE KIDNEY CELL 



ently, after one has allowed for the deduction of such changes as are 

 produced by the fixing agents generally. 



Leschke, and later, Oliver, found that urea was secreted in the prox- 

 imal convoluted tubules. The mitochondrial concentration is highest in 

 this part of the tubular apparatus, and the mitochondrial changes, which 

 by many have been thought to be of secretory importance, are also here 

 most pronounced. It is, therefore, only natural to attempt to link together 

 these observations. But the studies cited here lead me to believe that urea 

 feeding of various degrees does not influence beyond normal variations 

 the physical appearance of the mitochondrial apparatus of the kidney of 

 the white rat in general and of its proximal convoluted tubules in par- 

 ticular. 



Summary 



The result of an anatomical comparison between the kidneys of white 

 rats on a mixed diet, calling for no unusual renal activity, and the kidneys 

 of rats which for prolonged or brief periods of time had undergone a 

 markedly abnormal strain in the excretion of large amounts of urea, may 

 be summed up as follows : 



1. Prolonged urea feeding led to no increase in the size of the cells 

 of any part of the glomerulo-tubular apparatus. 



2. Neither a prolonged nor a brief increase in urea excretion had any 

 observable efTect on the appearance of the brush border. 



3. A careful study of the mitochondrial apparatus of the kidney 

 failed to show that variations in the rate of urea excretion during life 

 were associated with any change in the number, size or position of the 

 mitochondria. 



I take occasion to express my sincere appreciation to Dr. T. Addis 

 for his most helpful suggestions in editing this paper, to Miss Ella Wing 

 for her splendid help in the technical work, and to Dr. F. E. Blaisdell for 

 his kind advice in photographic difficulties. 



Stanford University Hospital, San Francisco 



