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G. C. Kennedy 



an increase in nuclei, or hyperplasia, and an increase of 

 cytoplasm, or hypertrophy. This method has shown that the 

 principal increase in the number of nuclei in the kidney of 

 the rat occurs during the first three months of life, pari passu 

 with the main growth of the skeleton, and this agrees well 

 with histological findings. 



There is a conflict of evidence about regeneration, however. 

 Rollason (1949) showed histologically that mitosis began in 

 the surviving kidney within forty-eight hours of unilateral 

 nephrectomy, whereas Mandel, Mandel and Jacob (1950) 



were unable to show any increase in kidney DNA even three 

 wrecks after the same operation. The difference apparently 

 depends on the age of the animals. Table I illustrates a 

 comparison made by the present author of the effect of 

 unilateral nephrectomy on the composition of the surviving 

 kidney in one-month, three-month and six-month-old rats. 

 In the youngest group, which were about the same age as 

 Rollason used, there was a rapid increase in DNA phosphorus. 

 In the middle group the DNA increased less than the RNA 

 and the nitrogen, and more slowly, as Mandel, Mandel and 

 Jacob had found. No hyperplasia at all occurred in the 



