INTRODUCTION 



109 



TABLE II 

 UREA-EXCRETING FUNCTION OF CONTROL AND UREA-FED RATS 



Controls 

 No. Urea in One Hour's Urea in lOOcc Ratio : Urea in Urine 



No. 



S 

 6 

 7 



The higher rate of urea excretion in spite of the lower level of blood urea 

 concentration in the urea-fed rats seems to indicate a greater facility in the excre- 

 tion of urea, in spite of the absence of any appreciable increase in the size of their 

 kidneys. But the number of experiments is much too small to allow for any 

 definite conclusion. 



The two groups of animals whose physiological history has been de- 

 scribed by Addis and Shevky were supplemented with another two groups 

 of white rats similar in age and weight. One group was fed general food 

 and the other was given urea food as noted in the life history of the tissues 

 of the first two groups. After several days' feeding, the first pair, urea- 

 fed and control, was killed. Then within two weeks a pair was killed 

 every other day. The idea was to obtain tissues for study of possible 

 early changes in the renal cellular structure produced by urea feeding for 

 a comparison with tissues from kidneys in a normal state of activity. 



There were, therefore, four distinct groups available for comparative 

 study; the first, composed of kidneys which since early youth had been 

 subjected to a constant strain in the excretion of large amounts of urea ; 

 the second, a group which had been fed a similar diet without urea but 

 had been given a single dose of urea just before death ; the third, a group 

 which was fed urea over a period of from two to fourteen days before 

 death ; and the fourth, a group fed on ordinary diet which received no 

 urea whatsoever. 



